Pharmacokinetics of gentamicin in the calf: developmental changes

The purpose of this study was to determine the pharmacokinetic values for gentamicin in neonatal calves and to compare these values with those in adult cattle (cows). Gentamicin (4 mg/kg of body weight) was administered IV to 7 Holstein bull calves on days 1 (between 12 and 24 hours of age), 5, 10, and 15 after birth, and was administered once IV to 7 Holstein cows. Serum was collected from each animal before administration and at 22 different time intervals from 2 to 400 minutes after injection. Sera were analyzed for gentamicin concentrations. Decay of serum gentamicin concentrations was best described by a 2-compartment pharmacokinetic model. Elimination half-life (t1/2 (beta)) of gentamicin decreased from day 1 (149 minutes) to day 5 (119 minutes), but did not change between days 5 and 15 (111 minutes). Compared with the t1/2(beta) in 1- and 15-day-old calves, the t 1/2 (beta) in cows was shorter (76 minutes). In the calves, apparent volume of distribution (based on total area under the disposition curve) did not change between 1 (393 ml/kg) and 5 (413 ml/kg) days of age, decreased on day 10 (341 ml/kg) and cows day 15 (334 ml/kg), and was markedly smaller than that in cows (140 ml/kg). Total body clearance of gentamicin in cows (1.29 ml/min X kg) was lower than that seen in calves on day 1 (1.92 ml/min X kg) and on day 15 (2.10 ml/min X kg). The decrease in apparent volume of distribution of gentamicin was mirrored by a large decrease in the extracellular fluid volume, as measured by inulin space.(ABSTRACT TRUNCATED AT 250 WORDS)     

Heritabilities and genetic correlations of growth and reproductive measurements in Hereford bulls

Weight, hip height, heart girth, pelvic height, pelvic width and scrotal circumference were measured at 403 and 490 d on 427 Hereford bulls. The bulls were members of a random-selection herd so estimates of genetic parameters should have a minimum of bias due to selection. Heritabilities and genetic correlations were estimated by normal paternal half-sib (PHS) correlation procedures. In addition, 256 son-sire pairs (RSS) were used to estimate heritabilities and genetic correlations by regression and covariance methods. The PHS method produced heritability estimates in the range of .41 to .58 for all measures at both ages, with the exceptions of hip height at 403 d (.24) and pelvic height at 490 d (.23). The estimates derived in the RSS method ranged from .10 to .60. The RSS relationship would contain a portion of any maternal X direct covariance effects. A difference in heritability estimated by the two methods could be a reflection of this covariance. Genetic correlations tended to be larger than phenotypic and, in several cases, were negative. The difference in the correlation between two measurements taken at 403 d vs the same correlation estimated at 490 d was not readily explainable but may be evidence for differences in maturation rates or maternal effects. Scrotal circumference had a positive genetic correlation with weight and heart girth and near 0 or negative genetic correlations with pelvic measures. Hip height had positive genetic correlations with weight and heart girth at 403 and 490 d and with pelvic measurements at 403 d, but the correlations were not as large at 490 d.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nonpuberal estrus and mature cow influences on growth and puberty in heifers

This experiment had two objectives. The first was to test a hypothesis that the presence of mature cows can influence the growth rate and physiological maturation rate of growing heifers. The second objective was to define a phenomenon termed nonpuberal estrus (NPE). Nonpuberal estrus in a prepuberal heifer is a behavioral estrus that is not followed by ovulation and formation of a corpus luteum. Two years of data were collected. All heifers were crossbred and were sired by Hereford, Charolais and Tarentaise bulls in yr 1 (n = 153) and by the same three breeds plus Jersey, Shorthorn, Brahman and Longhorn in yr 2 (n = 207). All heifers were born in the spring and weaned in October when approximately 180 d old. After weaning, heifers were assigned at random (within breed of sire) to control or mature cow (MC) treatment pens. Control pens contained 25 or 26 heifers and a sterile marker bull, while MC pens contained 25 or 26 heifers and a sterile marker bull plus four nonpregnant, mature cows. The presence of the mature cows did not (P greater than .10) affect rate of gain or yearling weight. Sire breed did (P less than .01) influence weight on test and average daily gain during the test in both years and affected (P less than .01) yearling weight during yr 2 but not (P greater than .10) during yr 1. A sire breed X treatment interaction effect on puberal traits was significant (P less than .01) in yr 1 but not in yr 2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fetal growth of beef calves. I. Effect of prepartum dietary crude protein on birth weight, blood metabolites and steroid hormone concentrations

Fifty-nine crossbred heifers (427 kg) bred to one Hereford sire were randomly assigned at 75 d prepartum to two diets. Heifers were individually fed, and diets were isocaloric but contained either a low (LP = 81% NRC, .56 kg/d) or high (HP = 141% NRC, .98 kg/d) level of crude protein. Jugular vein cannulae were inserted into 16 LP and 16 HP heifers at 10 prepartum. Daily preprandial blood samples that were collected until parturition were analyzed for serum estradiol-17 beta (E2), progesterone (P4), glucose (G) and urea nitrogen (UN). Heifers fed LP gained slower than HP-fed heifers before calving (.73 vs 1.02 kg/d; P less than .01); immediate post-calving weights and condition scores were 418 vs 444 kg (P less than .01) and 5.4 vs 6.1 (P less than .01; LP vs HP, respectively). Calf birth weights (35.3 vs 36.1 kg), average calving difficulty score (1.6 vs 1.6) and percent assisted births (35.5 vs 35.7%) did not differ (P greater than .10; LP vs HP, respectively). Prepartum concentrations of UN (6.2 vs 13.5 mg/dl) and G (52.9 vs 58.2 mg/dl) were lower (P less than .05) and P4 (5.94 vs 4.26 ng/ml) was higher (P approximately equal to .07) in LP heifers. Prepartum concentration profiles were related to calving difficulty score (CD, 1 = no assistance to 3 = hard pull) for E2 (CD1 vs CD2 + CD3, P less than .01; CD2 vs CD3, P approximately equal to .01), P4 (CD1 vs CD2 + CD3, P less than .05), G (CD1 vs CD2 + CD3, P less than .05) and UN (CD2 vs CD3, P less than .05). After calving, all dams were maintained together on pasture and supplemented with alfalfa hay and grain mix until adequate range forage was available to maintain weight gains. Dams that were fed LP prepartum gained faster than HP dams during this period (.49 vs .15 kg/d; P less than .01). Prebreeding weights (443 vs 453 kg; LP vs HP) and condition scores (5.1 vs 5.1) did not differ, nor was the postpartum interval affected (44 vs 40 d; LP vs HP). There was no effect of dietary protein on dystocia or postpartum interval, although there were diet-induced differences in body weight and condition of the dams at calving. Results indicate that differences in prepartum profiles of serum steroid hormones and metabolites may be related to dystocia, in addition to relative fetal oversize.     

Characterization of topcross progenies from Hereford, Limousin, and Piedmontese sires

Breeds of larger mature size tend to grow more rapidly and be older when attaining a given level of fatness. Hereford, Limousin, and Piedmontese are of approximately equal mature size and yet may vary in body composition at a given degree of maturity. However, direct comparisons among these three breeds were not found. Therefore, the objective of this research was to compare Hereford, Limousin, and Piedmontese progenies for economically important traits. Crossbred cows were bred to Hereford (n = 23), Limousin (n = 24), or Piedmontese (n = 24) sires. Male calves were either left intact or castrated at approximately 2 mo of age. Calves remained with their dams until weaning at an average age of 179 d. Male calves were then individually fed a growing ration until they reached 386 kg and then fed a finishing ration either 90 or 132 d. They were then slaughtered at a commercial abattoir and carcass data were collected. Female calves were group-fed and used to examine nutritional effects on age at puberty. Data were analyzed using REML and linear contrasts among the breed-of-sire effects evaluated. Herefordsired calves had shorter gestation periods and weighed less at birth than either Limousin- or Piedmontese-sired calves. Calving difficulty of Hereford- and Limousin-sired calves was less than that of Piedmontese-sired calves. Limousin-sired calves tended to grow more rapidly than Hereford-sired calves. By the finishing phase, Limousin- and Hereford-sired calves had greater average daily gains than Piedmontese-sired calves. Differences in dry matter intake among breeds of sire were relatively small. Differences in carcass weight, longissimus muscle area, fat depth, and percentage kidney, pelvic, and heart fat resulted in a clear stratification of USDA yield grade between breeds of sire. Differences in percentage primal cuts were similar to those for USDA yield grade. Hereford-sired calves had more marbling than progeny of Limousin or Piedmontese sires. However, the force necessary to shear cores from steaks of Piedmontese-sired calves was less than for progeny of Limousin or Hereford sires. Hereford- and Piedmontese-sired heifers were younger at puberty than Limousin-sired heifers. Within breeds of similar mature size and growth rate, ample variation exists in age at puberty and body composition at an approximately equal degree of maturity.