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PubMed2002

Breeding Opportunities for Increasing the Efficiency of Water Use and Crop Yield in Temperate Cereals.

Genetic advances in grain yield under rainfed conditions have been achieved by empirical breeding methods. Progress is slowed, however, by large genotype x season and genotype x location interactions arising from unpredictable rainfall, which is a feature of dry environments. A good understanding of factors limiting and/or regulating yield now provides us with an opportunity to identify and then select for physiological and morphological traits that increase the efficiency of water use and yield under rainfed conditions. The incorporation of these traits into breeders' populations should broaden their genetic base. It also may lead to faster selection methods and selection for the traits may result in correlated gains in yield. Here, we undertake a review of factors that limit yield in rainfed environments and discuss genetic opportunities and genetic progress in overcoming them. The examples given are for wheat (Triticum aestivum L.), but the principles apply to all cereal crops grown in dry environments.

Journal Article↗
PubMed2003

Increasing the yield of soluble recombinant protein expressed in E. coli by induction during late log phase.

Recombinant mammalian proteins expressed in E. coli can be difficult to purify in high yield in a soluble and functional form. Various techniques have been described to prevent proteolysis of expressed proteins and/or their sequestering as insoluble aggregates within inclusion bodies. We report conditions for expressing recombinant proteins from E. coli that significantly enhanced the yield of soluble and functional protein. We demonstrate high-yield recovery of a native, high-molecular-weight RNA binding protein without the aid of fusion protein sequence. The principle factor that increased protein yield was the induction of protein expression in a late log phase culture, although reduced temperature during the induction and a low IPTG concentration also contributed to a higher yield.

Cell Culture Techniques↗
PubMed2000

Yields and daily consumption of cigarettes in Japan in 1969-1996.

Cigarette modification trends and the relationship between nicotine yields and consumption in Japan were examined over the 27 years between 1969-1996. Data on cigarette use were obtained from reports published by the government and tobacco manufacturers. Over the study period, there has been a coherent pattern of cigarette modification in Japan. The sales-weighted average yields have declined from 20.7 mg tar and 1.64 mg nicotine/cigarette in 1969 to 8.7 mg tar and 0.72 mg nicotine/cigarette in 1996. On the other hand, the average daily consumption per smoker has continuously increased over the same period. Average nicotine yields and daily cigarette consumption have significant negative correlations among both males and females. This relationship was observed even after controlling for the price changes of cigarettes over time. It is indicated that smokers have compensated for reduced nicotine yields by increasing daily consumption. This may have offset potential benefits of the continuous decline in tar and nicotine yields to smokers' health.

Female↗
PubMed1995

Screening mammography in community practice: positive predictive value of abnormal findings and yield of follow-up diagnostic procedures.

OBJECTIVE: The purpose of this study was to gather from 50 community mammography practices that were included in the National Survey of Mammography Facilities data concerning abnormal findings on screening mammograms to determine the frequency of various recommendations made for patients who had abnormal findings and to compare these recommendations with the frequency with which the procedures were actually performed. We also determined the positive predictive value of screening mammograms (the number of cancers detected per 100 abnormal findings) and the yield (the number of cancers detected per 100 procedures done) of various diagnostic procedures done because of abnormal findings. MATERIALS AND METHODS: We identified 1717 screening mammograms done in the last half of 1991 that had abnormal findings. Radiologic recommendations and follow-up procedures, including repeat standard (screening) mammography, additional mammographic views, sonography, clinical breast examination, needle aspiration, needle biopsy, and open biopsy, were identified for all of the cases from the radiologic records, and follow-up data were obtained from referring physicians. The positive predictive value and yield in the National Survey of Mammography Facilities were compared with data from the mammography screening practice of the University of California at San Francisco (UCSF), a facility noted for its clinical efficiency. RESULTS: We estimate that 11% of all screening mammograms resulted in a recommendation for further diagnostic procedures. These 1717 mammograms with abnormal findings led to the following recommendations and procedures: repeat standard (screening) mammography, 610 (recommended)/635 (performed); additional mammographic views, 785/707; sonography, 400/345; biopsy, 189/229; and needle aspiration, 21/51. More procedures were done than were recommended in some cases because the results of certain procedures often led to the performance of other, additional procedures. The positive predictive value for screening examinations with abnormal findings was 3.5%, and the yield for open biopsy was 21%. In the UCSF data base, the positive predictive value for examinations with abnormal findings was 10%, and the yield for open biopsy was 34%. CONCLUSION: The positive predictive value for examinations with abnormal findings and the yield for diagnostic procedures performed as a result of abnormal findings in 50 community radiologic facilities were higher than those reported in some earlier studies, a fact that raised concern about the induced cost of screening mammography. However, these values were low compared with those in the UCSF data base. This fact was particularly true of repeat standard (screening) mammography.

Adult↗
PubMed2006

Effect of administration of a controlled-release monensin capsule on incidence of calving-related disorders, fertility, and milk yield in dairy cows.

OBJECTIVE: To determine the effect of a controlled-release monensin capsule administered at cessation of lactation on incidence of calving-related disorders, fertility, and milk yield in dairy cows. ANIMALS: 290 dairy cows treated with monensin and 290 untreated control cows. PROCEDURE: Treated cows received a capsule that released monensin at 335 mg/d for 95 days. Incidence of calving-related disorders; daily milk yield up to 20 days postpartum; test-day milk yield, fat, protein, and mature-equivalent 305-day milk production; and body condition score at calving were determined. Reproductive variables were conception rate at first service, pregnancy rate, and calving-to-conception interval. RESULTS: Cows treated with monensin were 2.1 times as likely to develop dystocia and 0.8 times as likely to develop metritis as control cows. For milk yield, there was an interaction of treatment X time X parity. In multiparous cows, monensin significantly improved milk yield at test days 4 and 7. In addition, monensin increased body condition score at calving. CONCLUSIONS AND CLINICAL RELEVANCE: Despite increasing the likelihood of developing dystocia and metritis, administration of monensin improved the lactational performance of multiparous cows and may be a promising additive for use at the time of cessation of lactation.

Animals↗
PubMed1992

Influence of genotype and yield and composition of milk on interval to first postpartum ovulation in milked beef and dairy cows.

Our objectives were to investigate the effects of genotype, yield and composition of milk, and changes in BW and body condition on the initiation of cyclic ovarian activity in nonsuckled beef and dairy cows milked twice daily. Nulliparous heifers were selected from three breeds, 12 Angus, 13 Simmentals, and 26 Holsteins, based on their EBV for milk yield. Cows were machine-milked twice daily, and daily milk yield was recorded; composite samples of milk were collected twice weekly for analyses of milk components. Blood was collected from all cows thrice weekly for 75 d postpartum, and concentrations of progesterone in serum measured by RIA were used to estimate day of first postpartum ovulation. Holstein cows produced more (P less than .05) milk (unadjusted or 3.5% fat-corrected) than Angus or Simmental cows during the first 30 d of lactation. Holstein cows had higher (P less than .01) peak yield of milk than Simmental and Angus cows. Days to peak milk yield were similar for Simmental and Holstein cows, and both were more (P less than .05) than those for Angus cows. Percentages of fat, protein, and total solids in milk were highest (P less than .05) for Simmental cows, whereas milk of Holstein cows had the highest (P less than .05) percentage of lactose and lowest (P less than .05) concentration of somatic cells. Average BW at ovulation differed (P less than .05) among breeds. Estimated daily changes in BW from calving to first ovulation were different (P less than .05) for Holstein and Simmental cows but were similar to those of Angus cows.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Quantitative influence of lysine and energy intake on yield of milk components in the primiparous sow.

A regression approach was used to assess quantitatively the influence of lysine and ME intake during lactation on yield of milk components and to determine whether this influence was mediated through precursor metabolite concentrations in the blood. The influence of lysine and energy intake on sow weight and backfat loss also was analyzed by linear regression. Twenty-three primiparous Landrace x Yorkshire sows were fed one of nine corn-soybean meal diets to achieve a matrix of lysine (15, 30, or 45 g/d) and ME (6.5, 11.5, or 16.5 Mcal/d) intakes. Sow BW and backfat losses were found to be predominantly controlled by ME intake (P less than .02), with no response to lysine intake (P greater than .92). Lysine and ME intake explained a smaller portion of the variability in milk component yield on d 8 (R2 less than .34) than on d 22 (R2 = .64 to .78), evidence that dietary effects of milk production increased as lactation progressed. Lysine and ME intake had an interactive influence (P less than .05) on yield of all milk components except lactose, demonstrating that the amount of lysine required to maximize milk production increased as ME intake increased. Strong relationships between diet and most blood precursor metabolite concentrations (R2 = .5 to .7) were detected on d 22. No obvious relationships between precursor metabolite concentrations and milk component yield (R2 = .05 to .2) were observed. These results describe quantitatively the prominent interactive effects of lysine and ME intake on yield of milk components and demonstrate that these effects are not directly associated with changes in precursor pool concentrations.

Adipose Tissue↗
PubMed1992

Estimates of subprimal yields from beef carcasses as affected by USDA grades, subcutaneous fat trim level, and carcass sex class and type.

One hundred beef carcasses were selected to represent the mix of cattle slaughtered across the United States. Selection criteria included breed type (60% British/continental European, 20% Bos indicus, and 20% dairy carcasses), sex class (beef and Bos indicus: 67% steers, 33% heifers; dairy: 100% steers), USDA quality grade (4% Prime, 53% Choice, and 43% Select), USDA yield grade (10% YG 1, 43% YG 2, 40% YG 3, and 7% YG 4), and carcass weight (steers: 272.2 to 385.6 kg, heifers: 226.8 to 340.2 kg). One side of each carcass was fabricated into boneless subprimals and minor cuts following Institutional Meat Purchase Specifications. After fabrication, subprimals were trimmed progressively of fat in .64-cm increments beginning with a maximum of 2.54 cm and ending with .64 cm. Linear regression models were developed for each individual cut, including fabrication byproduct items (bone, fat trim) to estimate the percentage yield of those cuts reported by USDA Market News. Strip loin, top sirloin butt, and gooseneck rounds from heifers tended to have a higher percentage yield at the same USDA yield grade than the same cuts from steers, possibly resulting from increased fat deposition on heifers. Percentage of fat trimmed from dairy steers was 2 to 3% lower than that from other sex-class/carcass types; however, due to increased percentage of bone and less muscle, dairy steers were lower-yielding. Fat trimmed from carcasses ranged from 7.9 to 15.6% as the maximum trim level decreased from 2.54 to .64 cm.

Adipose Tissue↗
PubMed1993

Contribution of breed, cow weight, and milk yield to the preweaning, feedlot, and carcass traits of calves in three beef breeding systems.

Data were obtained from 1980 to 1987 on animals belonging to one of three breeding systems: Hereford, small rotation, and large rotation. Differences among Angus-, Gelbvieh-, Pinzgauer-, and Tarentaise-sired calves within the small rotation system were generally not detected as significant for the preweaning traits of gestation length, calving ease, birth weight, gain to weaning, or creep feed intake with the exception of a longer gestation length for Gelbvieh-sired calves. Similarly, differences for feedlot gain, days on feed, feedlot intake, and the carcass characteristics of carcass weight and marbling, and lean, fat, and bone percentages were generally nonsignificant. Gelbvieh- and Pinzgauer-sired calves had higher growth rate, market weight, and longissimus muscle area than Angus- or Tarentaise-sired calves with a corresponding tendency for increased feed intake. Differences among Charolais-, Maine Anjou-, and Simmental-sired calves within the large rotation were not significant for any of the traits studied. Increased cow weight was positively associated with birth weight, significantly so for the small rotation. No patterns of association with cow weight were found for other preweaning traits. Increased milk yield was positively, but not always significantly, associated with gestation length and all weights and was negatively associated with creep intake. Neither cow weight nor milk yield showed any consistent association with feedlot or market traits, although increased milk yield was shown to be associated with higher daily gains for Hereford and small rotation and with higher carcass and market weights for Hereford. In general, associations of traits of calves with weight and milk yield of their dams were not detected as being different among breeding systems; except the effect of increased milk yield on gain to weaning was greater in Hereford than in large rotation cows.

Adipose Tissue↗
PubMed1995

Recombinant bovine somatotropin increases milk yield and calf gain in diverse breeds of beef cattle: associated changes in hormones and indices of metabolism.

In Exp. 1, Angus (A, n = 30), Charolais (C, n = 37), and Simmental (S, n = 30) multiparous cows received (s.c.) recombinantly derived bovine somatotropin (bST; sometribove, 500 mg) or vehicle (VEH) at 2-wk intervals from 124 to 228 d postpartum (DPP). Calves were weaned at 228 DPP. Bovine somatotropin increased (P < .01) milk yield and percentage of milk fat similarly in A, C, and S cows. Calf weaning weight was greater (P < .05) in cows treated with bST than in those given VEH. Administration of bST decreased deposition of fat and increased concentrations of IGF-I, insulin, glucose, and nonesterified fatty acids. In Exp. 2, we compared effects of bST initiated before or after the breeding season. Charolais (n = 33) and S (n = 40) cows were administered (at 2-wk intervals) VEH or bST beginning at 28 DPP (B-bST) or bST beginning at 105 DPP (A-bST). Calves were weaned at 243 DPP. Administration of bST before or after the breeding season increased milk yield on DPP 136 and 194; however, yields were greater in A-bST than in B-bST cows. Milk yields were similar in all cows at 236 DPP, corresponding to decreased forage availability. Calf body weight was greater (P < .05) in A-bST than VEH; B-bST calves were similar to VEH. Fat depth was greater in VEH than in bST-treated cows in C but not in S cows. Serum IGF-I was greater in A- and B-bST than in VEH cows. Mean days from calving to serum progesterone > 1 ng/mL and pregnancy rates were similar in VEH, A-, and B-bST cows. Administration of bST increased cow milk yield and subsequent calf weaning weight when initiated after 100 d postpartum. As anticipated, bST increased IGF-I, insulin, glucose, and nonesterified fatty acids. Administration of bST before and during the breeding season did not affect reproductive performance.

Animals↗
PubMed1995

The effect of caffeine on mammary gland development and milk yield in primiparous sows.

Pregnant Yorkshire gilts (n = 42) were fed caffeine (6 g/d) or served as controls from d 60 of pregnancy until d 4 postpartum to test the effect of caffeine on mammary gland development, milk yield, and feed consumption. Caffeine reduced voluntary feed intake (P = .001) and body weight gain (P = .001) of gilts from d 60 to 109 of gestation. Pig birth weight in the treated group was less than (P = .01) that in the control group. However, pig viability score at birth was not affected by maternal caffeine ingestion. For assessing mammary gland DNA, RNA, dry fat-free tissue (DFFT), fat, and protein content, four sows from the caffeine group and three controls were slaughtered on the 1st d of lactation. Immediately after slaughter, mammary systems were removed, separated by gland, and dissected free of skin, muscle, and fatty pad, which had not been invaded by glandular tissue. The DNA and RNA content were evaluated in DFFT. Caffeine increased mammary RNA content (P = .023) and milk yield (P = .001) on d 1 of lactation. However, DNA, DFFT, fat, and protein were not significantly increased, although values were somewhat greater in the treatment group (approximately 82%). On d 21 of lactation, milk yield of treated sows did not differ from that of controls. The increased milk yield on d 1 of lactation was due to increased mammary epithelial cell activity and cell numbers. These results indicate that caffeine feeding can have a positive effect on porcine mammary gland development as well as milk yield.

Aging↗
PubMed1996

Yields, chemical composition, and value of beef shank tissues obtained using Baader processing.

This experiment was designed to determine yield of meat and sinew from beef shanks processed with a Baader desinewing machine and to determine whether this process added value to a beef carcass. Baader desinewing machines use belt pressure against a rotating, perforated steel drum to separate tissues. Boneless beef shanks had 9.8% fat and 14.1 mg/g of collagen. Using the Baader with a 5-mm drum, the first pass lean yield was 73.3% and had fat reduced to 7.1% and collagen to 10.5 mg/g. Second-pass lean yield through the 5-mm drum was 19.6% and had 16.1% fat and 13.8 mg/g of collagen, leaving 6.7% separated sinew. Using a 3-mm drum reduced first-pass lean yield to 66.1% and reduced fat content to 5.8%. Second-pass lean yield, using 3- and 5-mm drums, was 26.1% and had 18.6% fat and 27.8 mg/g of collagen with 6.8% sinew. Desinewed lean is worth more than whole shanks. Furthermore, 95% lean is worth more than 90% lean, and the sinew also has a salvage value. Upgrading shanks with this desinewing device can increase the value of a beef carcass by $2.01 using a 5-mm drum or by $3.20 using both 3- and 5-mm drums.

Animals↗
PubMed1997

Influence of wholesale lamb marketing options and merchandising styles on retail yield and fabrication time.

Lamb carcasses (n = 94) from five packing plants, selected to vary in weight class and fat thickness, were used to determine retail yield and labor requirements of wholesale lamb fabrication. Carcasses were allotted randomly according to weight class to be fabricated as whole carcasses (n = 20), three-piece boxes (n = 22), or subprimals (n = 52). Processing times (seconds) were recorded and wholesale and retail weights (kilograms) were obtained to calculate retail yield. Subprimals were fabricated into bone-in retail cuts or boneless or semi-boneless retail cuts. Retail yield for subprimal lamb legs decreased from 85.3 +/- .6% for bone-in to 68.0 +/- .7% for a completely boneless retail product. Correspondingly, processing times increased from 126.1 +/- 5.4 s to 542.0 +/- 19.2 s for bone-in and boneless legs, respectively. For all subprimals, retail yield percentage tended to decrease and total processing time increase as cuts were fabricated to boneless or semi-boneless end points compared with a bone-in end point. Percentage retail yield did not differ (P > .05) among whole carcass, three-piece box, and subprimal marketing methods. Total processing time was shorter for subprimals (P < .05) than for the other two marketing methods.

Animals↗
PubMed1997

Phenotypic characterization of Rambouillet sheep expressing the callipyge gene: II. Carcass characteristics and retail yield.

Paternal half-sibling Rambouillet ram lambs (n = 18) representing two muscle phenotypes were slaughtered at 54.5 kg to evaluate carcass characteristics and composition. Lambs were produced from a sire that was heterozygous for the callipyge gene. Carcasses were broken into wholesale and retail cuts to evaluate percentage bone-in retail yield of carcasses at various fat trim levels and percentage of boneless retail cuts. Retail cuts were trimmed to .6 and then to 0 cm fat trim and bones were removed to determine boneless, closely trimmed retail cut yield. Chemical composition was determined using proximate analysis. Lambs expressing the callipyge gene had higher dressing percentages (57.3 vs 53.9), leg (14.4 vs 11.0) and conformation (14.4 vs 11.0) scores, and larger longissimus muscle (LM) areas (17.6 cm2 vs 10.3 cm2). All other carcass measurements were similar between phenotypes except marbling score, which was higher (417.8 vs 325.6) for controls. Lambs expressing the callipyge gene had a higher (40.2 vs 32.9) percentage boneless retail yield than controls. Retail yield of the boneless shoulder did not differ between phenotypes (8.9 vs 8.0). All other percentages of boneless retail cuts were higher (P < .02) for lambs expressing the callipyge gene. Carcasses from lambs with the callipyge gene had higher protein (16.6 vs 15.2), moisture (63.6 vs 58.6) and ash (.85 vs 77) percentages and lower fat (18.9 vs 25.4) percentages than controls. These data suggest that ram lambs expressing the callipyge gene have an advantage in retail yield and carcass conformation when compared to normal-muscled half-siblings.

Animals↗
PubMed1997

Characterization of different biological types of steers (cycle IV): wholesale, subprimal, and retail product yields.

Carcass cut-out yields of 888 steers obtained from mating Hereford and Angus cows to Hereford or Angus (HA), Charolais (Ch), Gelbvieh (Gb), Pinzgauer (Pz), Shorthorn (Sh), Galloway (Gw), Longhorn (Lh), Nellore (Ne), Piedmontese (Pm), and Salers (Sa) sires were compared. Data were evaluated at constant age (426 d), carcass weight (324 kg), fat thickness (1.2 cm), fat trim percentage (23%), and marbling (Small(00)) end points. Piedmontese-sired steers excelled in total retail product and fat trim percentages at all slaughter end points except at the 23% fat trim end point. At an age end point, percentage of retail product was greater in steers sired by Continental European breeds (Gb, Ch, Sa, Pz; 63.3 to 65.5% at 0 cm trim) than in steers sired by British breeds (Sh, HA; 60.1 to 61.0%). Piedmontese-sired steers, which were expected to carry one copy of a major gene for muscle hypertrophy, had the highest (P < .05) retail product yields at an age end point (69.7%). At an age end point, although carcass weights were significantly heavier (P < .05) for Charolais-sired steers than for Piedmontese-sired steers, lean growth rate, as reflected by totally trimmed retail product at 426 d, was similar (P > .05) for Piedmontese and Charolais-sired steers. Differences among sire breeds were small for retail product percentage at marbling, fat thickness, and fat trim end points. Ranking of sire breeds for age-constant weight of retail product was as follows: Ch, Pm, Gb, Sa, Ne, Pz, HA, Sh, Gw, and Lh. Sire breed differences in wholesale and subprimal cut yields were similar to total retail product differences. Piedmontese-sired steers produced the most muscular, leanest, and highest-yielding carcasses, and HA- and Sh-sired steers produced the fattest, lowest-yielding carcasses.

Analysis of Variance↗
PubMed1998

Retail yield and fabrication times for veal as influenced by purchasing options and merchandising styles.

Twenty-nine selected styles of subprimals or sections of veal were obtained from a commercial facility to assist in the development of a support program for retailers. They were fabricated into bone-in or boneless retail cuts and associated components by trained meat cutters. Each style selected (n = 6) was used to generate mean retail yields and labor requirements, which were calculated from wholesale and retail weights and processing times. Means and standard errors for veal ribs consisting of five different styles (n = 30) concluded that style #2, 7-rib 4 (10 cm) x 4 (10 cm), had the lowest percentage of total retail yield (P < .05) owing to the greatest percentage of bone. Furthermore, rib style #2 required the longest total processing time (P < .05). Rib styles #3, 7-rib chop-ready, and #5, 6-rib chop ready, yielded the greatest percentage of total retail yield and also had the shortest total processing time (P < .05). Within veal loins, style #2, 4 (10 cm) x 4 (10 cm) loin kidney fat in, had the greatest percentage fat (P < .05). Loin styles #2 and #3, 4 (10 cm) x 4 (10 cm) loin special trimmed, generated more lean and fat trimmings and bone, resulting in lower percentage of total retail yields than loin style #1, 0 (0 cm) x 1 (2.5 cm) loin special trimmed (P < .05). Results indicated that bone-in subprimals and sections required more processing time if fabricated into a boneless end point. In addition, as the number of different retail cuts increased, processing times also increased.

Animals↗
PubMed1998

Body composition at farrowing and nutrition during lactation affect the performance of primiparous sows: II. Milk composition, milk yield, and pig growth.

Sows that were either fat or lean at farrowing (340 or 280 g of body fat/kg BW, respectively) were offered either a low-protein (LP; 7.9% CP and 15.5 MJ DE/kg as fed) or a high-protein (HP; 19.0% CP and 15.6 MJ DE/kg as fed) diet on an ad libitum basis throughout a 4-wk lactation to test the hypothesis that the amount of milk and its composition are responsive to the supply of endogenous (body reserves) and exogenous (diet) substrates. Pigs were weighed at birth and weekly during lactation, milk yield was estimated using deuterium oxide in early (d 4 to 8) and late lactation (d 24 to 28), and milk samples were collected to determine composition in early (d 4 to 6) and late lactation (d 25 to 27). Throughout lactation, milk yield and composition were mainly associated with differences in litter size. Milk yield was about 15% higher in lean than in fat sows and in sows fed HP rather than LP, but large CV (17 to 32%) prevented these differences from attaining significance (P > .273). The responses in milk yield were reflected in pig growth. Differences in milk composition between treatment groups were not significant; however, during early lactation there was a tendency for fat sows to produce milk with a fat content 21% higher, and a protein content 12% lower, than that of lean sows. Changes in the protein:energy ratio of milk during the course of lactation and small changes in milk yield composition collectively suggested that in early lactation, sow body composition affected milk production but, as lactation progressed, the dietary supply of precursors for milk synthesis became more important.

Analysis of Variance↗
PubMed2001

Genetics of milk yield and fertility traits in Holstein-Friesian cattle on large-scale Kenyan farms.

Purebred Holstein-Friesian cows are the main exotic breed used for milk production on large, medium, and small farms in Kenya. A study was undertaken on seven large-scale farms to investigate the genetic trends for milk production and fertility traits between 1986 and 1997 and the genetic relationships between the traits. This involved 3,185 records from 1,614 cows, the daughters of 253 sires. There was a positive trend in breeding value for 305-d milk yield of 12.9 kg/ yr and a drop in calving interval of 0.9 d/yr over the 11-yr period. Bulls from the United States (U.S.) had an average total milk yield breeding value 230 kg higher than the mean of all bulls used; Canada (+121 kg), Holland (+15 kg), the United Kingdom (U.K., 0 kg), and Kenya (-71 kg) were the other major suppliers of bulls. Average breeding values of bulls for calving interval by country of origin were -1.31 (Canada), -1.27 (Holland), -0.83 (U.S.), -0.63 (Kenya), and 0.68 d (U.K.). The genetic parameters for 305-d milk yield were 0.29 (heritability), 0.05 (permanent environment effect as proportion of phenotypic variance) resulting in an estimated repeatability of 0.34. Using complete lactation data rather than 305-d milk yield resulted in similar estimates of the genetic parameters. However, when lactation length was used as a covariate heritability was reduced to 0.25 and the permanent environment effect proportion increased to 0.09. There was little genetic control of either lactation length (heritability, 0.09) or calving interval (heritability, 0.05); however, there were strong genetic correlations between first lactation milk yield, calving interval, and age at first calving.

Animal Husbandry↗