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Biomedical subjects

T G Jenkins

Publications and source records attributed to T G Jenkins.

47 records · Page 3Linked to original sources
PubMed1987

Feeding behavior characteristics of intact male lambs as affected by number of lambs in a pen with restricted access to the feed stall.

To investigate the effect of number of animals housed in a pen upon feed intake, 72 intact male lambs were randomly assigned to treatments consisting of 3, 7, 11 or 15 animals/pen in each of two trials. For each animal's feeding event, length of feeding (s) and feed consumption (g) were recorded through use of an automatic feeding system. This system allows one animal to feed at a time. Pens were treated as experimental units with observations repeated daily for 21 d. Response variables were feed consumption (g), time (s) and rate of feed consumed (g/s) per visit and feed consumption (g), average time (s) and number of visits per animal daily. Number of animals/pen was significant for most feeding behavior characteristics. As number of lambs within a pen increased, feed consumption/visit increased linearly in both trials. For Exp. 1, rate of feed consumption/visit increased at a decreasing rate, while in Exp. 2 only the linear effect of lamb numbers on this trait was significant. Daily feed consumption/lamb was greatest for intermediate lamb numbers, and the number of visits and time spent feeding/lamb decreased as the number of lambs within a pen increased. Results suggest that the feeding behavior of ram lambs with restricted access to a feeding stall can be modified by the number of lambs housed in a pen.

Animals↗
PubMed1987

Prenatal androgen exposure and growth and secretion of growth hormone and prolactin in ewes postweaning.

Growth and secretion of growth hormone (GH) and prolactin (PRL) in ewe lambs exposed to androgen during fetal development were investigated. Testosterone cypionate was administered to the pregnant dams from approximately Days 28 to 84 of gestation. Ewe lambs from dams that received androgen exhibited masculinized external genitalia and some masculine behavioral characteristics. Intact androgenized ewe lambs grew faster (P less than 0.05) and were more efficient in conversion of food to body gain (P less than 0.05) than ewe lambs born to untreated dams over the period from 70 to 224 days of age. One-half of the ewe lambs in each group was ovariectomized at 58 days of age. Ovariectomy had no effect on subsequent growth or efficiency of growth in the control ewe lambs. However, ovariectomy of androgenized ewe lambs abolished the observed stimulated rate of growth and decreased the improvement in efficiency of food conversion. Blood samples were collected from the lambs at 85 and 136 days of age at 15-min intervals for 8 hr to determine parameters of GH and PRL secretion. Prenatal androgen exposure had no effect on any parameter of GH or PRL secretion. These data indicate that prenatal androgen exposure altered differentiation of growth potential in ewe lambs, but the growth response was not mediated through dramatic changes in secretion of adenohypophysial somatotropic hormones, GH and PRL.

Animals↗
PubMed1986

Characterization of cattle of a five-breed diallel: VI. Fat deposition patterns of serially slaughtered bulls.

Dissection and chemical analysis data from 197 bulls of 15 breedtypes were used to examine the distribution of total fat (TOTFAT) among carcass fat (CFAT), viscera fat (VIF), kidney plus pelvic fat (KPF) and blood fat (BLF). The bulls were obtained from a five-breed diallel involving Angus, Brahman, Hereford, Holstein and Jersey; reciprocal crosses were pooled. One or two bulls of each breedtype were slaughtered at each of seven ages: 6, 9, 12, 15, 18, 24 and 30 mo. An allometric equation was utilized to describe growth rate of each fat depot relative to either TOTFAT or carcass side weight (CSW). The pooled within-breedtype differential growth rates obtained from the allometric equation indicated that as TOTFAT or CSW increased, the proportion composed of CFAT and KPF increased (growth coefficients significantly greater than 1), whereas the proportion composed of VIF and BLF decreased (growth coefficients significantly less than 1). Holstein and Jersey tended to have more CFAT than Hereford, Angus and Brahman. Jersey had more KPF than other breeds. Crossbreds exhibited positive heterosis for CFAT and VIF, and negative heterosis for KPF. On a constant CSW basis, there were no significant breedtype differences in TOTFAT: nevertheless, differences in fat distribution among breedtypes persisted. There were different amounts of fat at the depots studied, but fat growth coefficients relative to TOTFAT tended to be homogeneous among breedtypes.

Adipose Tissue↗
PubMed1986

Effects of breed type and restricted versus ad libitum feeding on fatty acid composition and cholesterol content of muscle and adipose tissue from mature bovine females.

Fatty acid composition and cholesterol content of muscle and adipose tissue from mature cows (N = 101) representing 15 breeds and crosses were determined. An initial group of cows was slaughtered after being fed slightly above the maintenance level for 2 wk; the remaining cows were fed either at the maintenance level or ad libitum for 84 d, then slaughtered. Samples of triceps brachii and longissimus muscle and subcutaneous and perinephric adipose tissue were obtained from each carcass. In addition, phospholipid and triacylglycerol fatty acids from total lipid extracts of triceps brachii muscle and subcutaneous adipose tissue were analyzed for 24 cows that were fed ad libitum or at the maintenance level for 84 d. Breed type effects on fatty acid composition were more pronounced in adipose tissue than in muscle tissue. Total lipid extracts of both triceps brachii and longissimus muscle from animals fed a maintenance diet for 84 d contained higher (P less than .01) percentages (3 to 8%) of polyunsaturated fatty acids (PUFA) and lower percentages (2 to 3%) of saturated fatty acids (SFA) than those from animals fed ad libitum for 84 d. This reflected significant variation in the fatty acids C14:0, C16:0, C18:2, C18:3 and C20:4 for both longissimus and triceps brachii muscle. Fatty acid composition within phospholipid and triacylglycerol fractions was similar regardless of maintenance or ad libitum feeding. Much of the variation in total lipid fatty acid composition appeared to be the result of differences in triacylglycerol:phospholipid ratios. Adipose tissue contained about twice as much cholesterol (mg/100 g wet weight) as muscle tissue. Both breed type and feeding group effects on cholesterol content of muscle tissue were nonsignificant. Values for cholesterol content of adipose tissue from cows fed restricted diets were higher than those from cows fed ad libitum (approximately 55 mg/100 g higher for subcutaneous and 25 mg/100 g for perinephric). The results show that changes in fatty acid composition of bovine tissues can be made genetically and by varying the energy level in the diet. Alteration of the cholesterol content of muscle tissue by these methods does not appear to be feasible.

Adipose Tissue↗
PubMed1986

Postweaning performance and carcass characteristics of crossbred ewe lambs produced in accelerated or annual lambing systems.

Weaning, postweaning and carcass characteristics of ewe lambs were analyzed to determine if significant interactions occurred among management options. Management options considered were type of lambing system, choice of maternal and terminal sire lines and month of birth within lambing system. In general, significant interactions were not observed, suggesting production (output) characterizations for the postweaning period can be extended across management options. The experimental protocol associated with the types of lambing system resulted in a highly significant effect of lambing system upon all characteristics, especially in relation to age, weight and feed consumption characteristics prior to slaughter. Suffolk-sired lambs tended to be heavier for most weight characteristics, fatter and have higher carcass quality and leg conformation scores relative to Columbia-sired lambs. Differences of fraction of Finn sheep (Finn, .50 vs .25) of the dam were not noted, with the exception of weaning weight (21.2 +/- .28 and 22.2 +/- .27 kg, respectively) and carcass quality and leg conformation scores. Within the annual lambing season, lambs born in March and April were heavier at weaning, consumed less feed and required less weight gain to attain market weight than lambs born in May. Lambs from the May lambing had significantly higher gross feed efficiency ratios. Within the accelerated lambing system, the lambs born in January to February period tended to be heavier than lambs from the other lambing periods. Observed differences among month of lambing within lambing system for other characteristics were not consistent.

Adipose Tissue↗
PubMed1985

Cow type and the nutritional environment: nutritional aspects.

Numerous studies have been reported that relate to the influence of cattle type on production efficiency; however, most reported studies have been concerned with output characteristics. This review concentrates on the influence of cattle type on the input requirements and more specifically, energy requirements. Data are presented that show that energy is required for maintenance, growth, gestation and lactation and requirements for each of these functions vary among cattle types. Data are presented that suggest 70 to 75% of total annual energy requirements are required for maintenance functions and variation in requirements for maintenance appear to be greater than variation in requirements for growth, gestation or lactation. In general, variation in maintenance requirements appears to be positively associated with genetic potential for measures of production, e.g., rate of growth or milk production. Reported results suggest that animals having genetic potential for high productivity may have less advantage or be at a disadvantage in a more restrictive environment, suggesting the need for synchronization of production environment and germ plasm resources. Some of the sources of variation in maintenance requirements have been discussed. Data are cited that suggest little of the variation in maintenance energy expenditures is attributable to variation in total body composition per se. However, considerable evidence has accumulated to show that a relatively large proportion of maintenance energy expenditures can be attributed to energy expenditures of visceral organs, especially the liver and gastrointestinal tract. High rates of energy expenditures of these tissues appear to be directly or indirectly associated with the high rates of protein synthesis in these tissues. Greater use of differing research approaches and assimilation of the results are needed to develop an understanding of the reasons for variation among animals in maintenance energy expenditures or energetic efficiency.

Animal Feed↗
PubMed1984

Relationships among various body components of mature cows.

Mature (9-yr-old), nonpregnant, nonlactating Angus X Hereford and the reciprocal cross (AHX, 12), Charolais X Angus or Hereford (CX, 11), Jersey X Angus or Hereford (JX, 11) and Simmental X Angus or Hereford (SX, 12) cows that had been fed either a low (112 kcal X kg-.75 X d-1), medium (178 kcal X kg-.75 X d-1) or high (ad libitum) level of metabolizable energy (ME) intake for 140 d were used to evaluate relationships among various body components. Live weight, hip height, backfat and condition score were determined on d 140. Before slaughter, each cow was infused with deuterium oxide (D2O; .25 g/kg live weight) and serial blood samples were taken. Traits evaluated after slaughter were hot weight of each carcass half, hide weight, viscera weight, longissimus muscle area, fat thickness, kidney, pelvic and heart fat percentage and marbling score. Offal and carcass chemical compositions were determined and empty body composition was calculated. Moderate to high (R2 = .82 to .97) coefficients of determination were obtained when weight of empty body chemical components were regressed on live animal or carcass cooler measures. Correlations between percentage carcass or empty body water and percentage of fat, fat-free organic matter or energy, or between amount of carcass or empty body water and amount of fat-free organic matter were high (R2 = .83 to .99). Weight of carcass or empty body water was not highly related (R2 = .05 to .22) to the total amount of fat or energy. Similar results were obtained when amount of empty body components were regressed on D2O spaces alone. Inclusion of empty body weight (or live weight) in equations relating D2O spaces to weight of the empty body or chemical components resulted in R2 values of .86 to .99. Carcass composition, as expected, was more highly related to empty body composition than was offal composition. Empty body composition was not highly related to empty body weight.

Adipose Tissue↗
PubMed1984

Energy utilization by mature, nonpregnant, nonlactating cows of different types.

Four types of crossbred cows were used in each of two studies designed to estimate the metabolizable energy (ME) required to maintain weight or energy equilibrium of mature (9-yr-old), nonpregnant, nonlactating cows. The four cow types were chosen to represent cow types having moderate mature size-moderate milk production potential (Angus X Hereford, Hereford X Angus; AHX), large mature size-moderate milk production potential (Charolais X Angus or Hereford; CX), small mature size-high milk production potential (Jersey X Angus or Hereford; JX) and large mature size-high milk production potential (Simmental X Angus or Hereford; SX). In each of two consecutive years, four cows of each type were assigned randomly and fed individually either a low (113 kcal ME X kg-.75 X d-1), medium (178 kcal ME X kg-.75 X d-1) or a high (ad libitum) level of a corn silage-based diet for 140 d. Body composition of each cow was estimated by deuterium oxide dilution techniques at d 0 and 140 of each study and gains were calculated. The ME required to maintain weight or energy equilibrium was estimated for each type of cow. Estimates of ME required to maintain energy equilibrium (from the regression of log heat production, kcal X kg-.75 X d-1 on ME intake kcal X kg-.75 X d-1) were 130, 129, 145 and 160 kcal X kg-.75 X d-1 for AHX, CX, JX, and SX cows, respectively. Similar trends were observed when other models were used. Cow types with higher milk production potential had higher maintenance (kcal X kg-.75 X d-1) than cows with lower milk production potential. Cows of larger size had maintenance requirements (kcal X kg-.75 X d-1) similar to those of smaller size. Possible reasons for these differences as well as their potential impact on cow efficiency are discussed.

Animals↗
PubMed1983

Nutrient requirements to maintain weight of mature, nonlactating, nonpregnant cows of four diverse breed types.

Four breed types with 12 cows/breed-type (Hereford x Angus, AHx; Charolais and Angus and Charolais x Hereford, Cx; Jersey x Angus, Jersey x Hereford, Jx and Simmental x Angus, Simmental x Hereford, Sx) were used to estimate nutrient requirements for zero daily weight change. Four nonpregnant, nonlactating cows of each breed type were assigned to one of three feeding levels [90 kcal metabolizable energy (ME).kg body wt (kg)-.75 . d-1, 150 kcal ME.kg-.75.d-1 and ad libitum] for a 140 d feeding period. The feeding trial was: Period 1 (d 0 to 70) and Period 2 (d 70 to 140). Effect of breed type, feeding level and the two-way interaction upon weight, weight change and feed intake data were initially analyzed. Two-factor interactions tended not to be significant for weight and weight change. The main effects of breed type and feeding level tended to be significant for weight and weight change in each of the periods. On d 0, the Sx (570 +/- 13 kg) and Cx (578 +/- 14 kg) were heavier (P less than .05) than the AHx (527 +/- 13 kg) all of which were heavier than the Jx (458 +/- 14 kg). Under the two restricted diets, the breed type ranking for dry matter intake corresponded to the ranking for initial body weight. However, at the ad libitum feeding level, the Cx tended to consume less dry matter than the other breed types. Measures of weight change were evaluated to test the effect of breed type and dry matter intake. The effect of breed type was significant only for daily weight change (kg/d) during Period 2. The linear and(or) quadratic effects of dry matter intake (2.53 Mcal ME/kg dry matter) on measures of weight change were significant in all periods. During Period 1, the pooled dry matter intake estimate for zero daily weight change and zero metabolic weight change were 8.1 kg/d and 75.3 g.kg-.75.d-1, respectively. For AHx, Cx, Jx and Sx during Period 2, daily dry matter intake for zero weight gain was 4.2, 5.3, 4.2 and 5.5 kg/d, respectively. A pooled estimate of 43.9 g . kg-.75 . d-1 was obtained for dry matter intake relative to metabolic size in Period 2.

Animals↗
PubMed1981

Plasma growth hormone, prolactin and thyrotropin secretory patterns in Hereford and Simmental calves.

An experiment was conducted to test the hypothesis that bull calves of a larger, faster growing breed of cattle exhibit greater secretory activity of anabolic pituitary hormones than bull calves of a smaller, slower growing breed. Calves of both breeds were raised under similar conditions and maintained on the same diet for approximately 4 weeks before the blood sampling period. Simmental bull calves had higher (P less than .01) average daily gains and a heavier (P less than .01) mean body weight than Hereford bull calves. Overall plasma growth hormone (GH) concentrations were higher (P less than .01) in Simmental bull calves than in Hereford bull calves. Mean baseline GH was also higher (P less than .05) in Simmentals. Overall and baseline concentrations of prolactin (PRL) were similar for both breeds. Mean amplitude of PRL secretory spikes was higher (P less than .05) for Simmental than for Hereford bull calves. There was no breed effect on any variable of thyrotropin secretion. These data suggest that representatives of a larger, faster growing breed of cattle (Simmental) exhibit greater secretory activity of GH and PRL than do representatives of a smaller, slower growing breed (Hereford).

Animals↗