Effects of poor maternal diet during gestation are detected in F2 offspring.

Poor maternal nutrition of F0 ewes impairs F1 offspring growth, with minimal differences in glucose tolerance or select metabolic circulating factors, and independent of differences in residual feed intake (RFI). To determine if poor maternal nutrition in F0 ewes alters F2 offspring growth, circulating leptin, feed efficiency, or glucose tolerance, F0 ewes (n = 46) pregnant with twins were fed 100% (control), 60% (restricted), or 140% (over) of National Research Council requirements from days 30 ±â€…0.02 of gestation until parturition. At 16 to 19 mo of age, female F1 (n = 36) offspring were bred to generate F2 offspring [CON-F2 (n = 12 ewes; 6 rams), RES-F2 (n = 7 ewes; 13 rams), or OVER-F2 (n = 13 ewes; 9 rams) corresponding to diets of the granddam (F0)]. Lamb body weights (BW) and blood samples were collected weekly from days 0 to 28 and every 14 d until day 252 of age. Circulating leptin was measured in serum at days 0, 7, 14, 56, 210, and 252. An intravenous glucose tolerance test was performed at days 133 ±â€…0.28. At days 167 ±â€…0.33, individual daily intake was recorded over a 77-d feeding period to determine RFI. Rams were euthanized at days 285 ±â€…0.93, and body morphometrics, loin eye area (LEA), back fat thickness, and organ weights were collected and bone mineral density (BMD) and length were determined in the right hind leg. During gestation, OVER-F1 ewes tended to be 8.6% smaller than CON-F1 ewes (P ≤ 0.06). F2 offspring were of similar BW from birth to day 70 (P ≥ 0.20). However, from days 84 to 252, RES-F2 offspring tended to be 7.3% smaller than CON-F2 (P ≤ 0.10). Granddam diet did not influence F2 ram body morphometrics, organ or muscle weights, LEA, adipose deposition, or leg BMD (P ≥ 0.84). RES-F2 (-0.20) and CON-F2 (-0.45) rams tended to be more feed efficient than CON-F2 ewes (0.31; P ≤ 0.08). No effects of granddam diet were observed on glucose or insulin average or baseline concentrations, area under the curve, first-phase response, or ratio (P ≥ 0.52). However, CON-F2 rams (297 mg/dL ±â€…16.5) had a greater glucose peak compared with RES-F2 rams (239 mg/dL ±â€…11.2; P = 0.05). Peak insulin concentrations were not influenced by granddam diet (P = 0.75). At d 56, RES-F2 and OVER-F2 offspring had 53.5% and 61.8% less leptin compared with CON-F2 offspring, respectively (P ≤ 0.02). These data indicate that poor maternal nutrition impacts offspring growth into the second generation with minimal impacts on offspring RFI, glucose tolerance, and circulating leptin.

Survey of the use of beef semen in dairy herds in Pennsylvania and nearby states.

Because dairies across the United States have rapidly adopted breeding to beef breed sires, the use of beef semen has increased dramatically in recent years. The objective of this survey was to gather information about the use of beef semen by dairy producers in the Northeast United States to generate beef × dairy cattle for beef markets. The survey was conducted using the services of the Center for Survey Research at the Pennsylvania State University-Harrisburg campus. Respondents had two options for returning their responses: 1) mail the paper survey to CSR in the postage-paid business-reply envelope included in the mailing, or 2) complete the survey online via an open-access web survey link. A total of 669 surveys were received and a final number of 617 surveys were included in the responses based on completeness and validity of the responses. Because of the broad electronic distribution, a true response rate cannot be calculated. Of these, 463 (75.0%) were completed via returned paper survey, and 154 (25.0%) were completed via web, between November 9, 2021 and February 16, 2022. Of the 617 respondents, 539 were from Pennsylvania. Due to the large variations in returned survey copies by state, results are reported without state separation. Across all respondents, 69.7% reported milking 100 or fewer cows and over 90% of collected responses reported Holsteins as the predominant dairy breed in the Northeast. Only 18.8% of the respondents did not currently, nor plan to, breed with beef semen. Deciding which beef bulls to use on Northeast dairy farms was primarily based on the recommendation of the semen sales representative (54.5%) and the price of the semen purchased (42.3%). In addition, 89.7% of respondents cited using Angus genetics in their beef bull selections. However, there was no difference in reported profitability of crossbreeding between respondents who indicated using other beef breeds vs. those who indicated just using Angus (P ≥ 0.19). In conclusion, using beef sires on dairy females, regardless of the breed of beef sire, adds value to the resulting progeny from dairy farms in the Northeast.

Effects of poor maternal nutrition during gestation on ewe and offspring plasma concentrations of leptin and ghrelin.

Poor maternal nutrition during gestation can negatively affect offspring growth, development, and health. Leptin and ghrelin, key hormones in energy homeostasis and appetite control, may mediate these changes. We hypothesized that restricted- and over-feeding during gestation would alter plasma concentrations of leptin and ghrelin in ewes and offspring. Pregnant ewes (n = 37) were fed 1 of 3 diets starting on d 30 ± 0.02 of gestation until necropsy at d 135 of gestation or parturition: restricted- [RES; 60% National Research Council (NRC) requirements for total digestible nutrients, n = 13], control- (CON; 100% NRC, n = 11), or over-fed (OVER; 140% NRC, n = 13). Blood samples were collected from pregnant ewes at days 20, 30, 44, 72, 100, 128, and 142 of gestation. Offspring blood samples were collected within 24 h after birth (n = 21 CON, 25 RES, 23 OVER). Plasma leptin and ghrelin concentrations were determined by RIA. Ewe data were analyzed using the MIXED procedure in SAS with ewe as the repeated subject. Offspring data were analyzed using the MIXED procedure. Correlations between BW and leptin and ghrelin concentrations were identified using PROC CORR. At d 100, RES (5.39 ± 2.58 ng/mL) had decreased leptin concentrations compared with OVER (14.97 ± 2.48 ng/mL; P = 0.008) and at d 128, RES (6.39 ± 2.50 ng/mL) also had decreased leptin concentrations compared with OVER (13.61 ± 2.47 ng/mL; P = 0.04). At d 142, RES (0.26 ± 0.04 ng/mL) had increased ghrelin concentrations compared with CON (0.15 ± 0.04 ng/mL; P = 0.04). Leptin and ghrelin concentrations were also altered between days of gestation within a dietary treatment. In CON ewes, plasma concentrations of leptin were increased at d 30 (19.28 ± 7.43 ng/mL) compared with d 44 (5.20 ± 3.10 ng/mL; P = 0.03), and the plasma concentrations of ghrelin at d 128 (0.20 ± 0.03 ng/mL) were increased compared with d 30 (0.16 ± 0.03 ng/mL; P = 0.01) and d 100 (0.17 ± 0.03 ng/mL; P = 0.04). Maternal diet did not alter plasma ghrelin or leptin concentrations in the offspring (P > 0.50). There were no strong, significant correlations between ewe BW and leptin (r < 0.33; P > 0.06) or ghrelin (r > -0.47; P > 0.001) concentrations or lamb BW and leptin or ghrelin concentrations (r > -0.32, P > 0.06). Maternal alterations in circulating leptin and ghrelin may program changes in energy balance that could result in increased adiposity in adult offspring. Alterations in energy homeostasis may be a mechanism behind the long-lasting changes in growth, body composition, development, and metabolism in the offspring of poorly nourished ewes.

PHYSIOLOGY AND ENDOCRINOLOGY SYMPOSIUM:The effects of poor maternal nutrition during gestation on offspring postnatal growth and metabolism.

Poor maternal nutrition during gestation has been linked to poor growth and development, metabolic dysfunction, impaired health, and reduced productivity of offspring in many species. Poor maternal nutrition can be defined as an excess or restriction of overall nutrients or specific macro- or micronutrients in the diet of the mother during gestation. Interestingly, there are several reports that both restricted- and over-feeding during gestation negatively affect offspring postnatal growth with reduced muscle and bone deposition, increased adipose accumulation, and metabolic dysregulation through reduced leptin and insulin sensitivity. Our laboratory and others have used experimental models of restricted- and over-feeding during gestation to evaluate effects on early postnatal growth of offspring. Restricted- and over-feeding during gestation alters body size, circulating growth factors, and metabolic hormones in offspring postnatally. Both restricted- and over-feeding alter muscle growth, increase lipid content in the muscle, and cause changes in expression of myogenic factors. Although the negative effects of poor maternal nutrition on offspring growth have been well characterized in recent years, the mechanisms contributing to these changes are not well established. Our laboratory has focused on elucidating these mechanisms by evaluating changes in gene and protein expression, and stem cell function. Through RNA-Seq analysis, we observed changes in expression of genes involved in protein synthesis, metabolism, cell function, and signal transduction in muscle tissue. We recently reported that satellite cells, muscle stem cells, have altered expression of myogenic factors in offspring from restricted-fed mothers. Bone marrow derived mesenchymal stem cells, multipotent cells that contribute to development and maintenance of several tissues including bone, muscle, and adipose, have a 50% reduction in cell proliferation and altered metabolism in offspring from both restricted- and over-fed mothers. These findings indicate that poor maternal nutrition may alter offspring postnatal growth by programming stem cell populations. In conclusion, poor maternal nutrition during gestation negatively affects offspring postnatal growth, potentially through impaired stem and satellite cell function. Therefore, determining the mechanisms that contribute to fetal programming is critical to identifying effective management interventions for these offspring and improving efficiency of production.

Ultrasound during mid-gestation: Agreement with physical foetal and placental measurements and use in predicting gestational age in sheep.

To determine the effects of poor maternal nutrition and litter size on foetal growth during mid-gestation, pregnant ewes (n = 82) were fed 100%, 60% or 140% of NRC TDN beginning at day 30.2 ± 0.2 of gestation. Transabdominal ultrasound was performed weekly between day 46.0 ± 0.4 and 86.0 ± 0.7 to monitor foetal heart width (HW), umbilical diameter (UMB), rib width (RW) and placentome outer (OD) and inner diameter (ID). Data were analysed with repeated-measures using the mixed procedure for effects of maternal diet, litter size and gestation, and equations predictive of gestational age were generated using the regression procedure. To determine the agreement of ultrasound measurement and actual size, ewes (n = 20-21) were euthanized at day 45 or 90 to obtain corresponding postmortem measurements for Bland-Altman analysis. The HW, UMB and placentome OD and ID increased with gestation (p < .0001) but were unaffected by maternal diet or litter size (p ≥ .12). Ultrasound underestimated postmortem measurements of HW (14.8%), UMB (7.3%), placentome OD (4.5%) and ID (37.3%) at day 90 of gestation. Ultrasound underestimated RW at day 45 (7.7%) but overestimated RW (23.8%) at day 90, indicating inconsistent bias when reporting RW by ultrasound. Combining the HW, UMB, RW and placentome OD generated the strongest equation predictive of gestational age (R2  = .91). These findings indicate that during mid-gestation, maternal diet or litter size did not affect HW, UMB or placentome diameters and these factors can be used to estimate gestational age.

Fetal and organ development at gestational days 45, 90, 135 and at birth of lambs exposed to under- or over-nutrition during gestation,.

To determine the effects of poor maternal nutrition on offspring body and organ growth during gestation, pregnant Western White-faced ewes (n = 82) were randomly assigned into a 3 × 4 factorial treatment structure at d 30.2 ± 0.2 of gestation (n = 5 to 7 ewes per treatment). Ewes were individually fed 100% (control), 60% (restricted) or 140% (over) of NRC requirements for TDN. Ewes were euthanized at d 45, 90 or 135 of gestation or underwent parturition (birth) and tissues were collected from the offspring (n = 10 to 15 offspring per treatment). Offspring from control, restricted and overfed ewes are referred to as CON, RES and OVER, respectively. Ewe data were analyzed as a completely randomized design and offspring data were analyzed as a split-plot design using PROC MIXED. Ewe BW did not differ at d 30 (P ≥ 0.43), however restricted ewes weighed less than overfed and overfed were heavier than controls at d 45, and restricted weighed less and overfed were heavier than controls at d 90 and 135 and birth (P ≤ 0.05). Ewe BCS was similar at d 30, 45 and 90 (P ≤ 0.07), however restricted ewes scored lower than control at d 135 and birth (P ≤ 0.05) and over ewes scored higher than control at d 135 (P ≤ 0.05) but not at birth (P = 0.06). A maternal diet by day of gestation interaction indicated that at birth the body weight (BW) of RES offspring was less than CON and OVER (P ≤ 0.04) and heart girth of RES was smaller than CON and OVER (P ≤ 0.004). There was no interaction of maternal diet and day of gestation on crown-rump, fetal, or nose occipital length, or orbit or umbilical diam. (P ≥ 0.31). A main effect of maternal diet indicated that the RES crown-rump length was shorter than CON and OVER (P ≤ 0.05). An interaction was observed for liver, kidney and renal fat (P ≤ 0.02). At d 45 the liver of RES offspring was larger than CON and OVER (P ≤ 0.002), but no differences observed at d 90, 135 or birth (P ≥ 0.07). At d 45, the kidneys of OVER offspring were larger than CON and RES (P ≤ 0.04), but no differences observed at d 90, 135 or birth (P ≥ 0.60). At d 135, OVER had more perirenal fat than CON and RES (P ≤ 0.03), and at birth RES had more perirenal fat than CON and OVER (P ≤ 0.04). There was no interaction observed for offspring heart weight, length or width, kidney length, adrenal gland weight, loin eye area or rib width (P ≥ 0.09). In conclusion, poor maternal nutrition differentially alters offspring body size and organ growth depending on the stage of gestation.

Poor maternal nutrition during gestation alters the expression of genes involved in muscle development and metabolism in lambs.

Poor maternal nutrition during gestation can result in reduced muscle mass and increased adiposity of the muscle tissue in the offspring. This can have long-lasting consequences on offspring health and productivity. However, the mechanisms by which poor maternal nutrition affects postnatal muscle development are poorly understood. We hypothesized that poor maternal nutrition during gestation would alter expression of key pathways and genes involved in growth, development, and maintenance of the muscle of lambs. For this study, beginning at d 31 ± 1.3 of gestation, ewes were fed 100 (control), 60 (restricted), or 140% (overfed) of the NRC requirements. Within 24 h of birth, lambs were necropsied and semitendinosus muscle tissue was collected for gene expression analysis. Using RNA sequencing (RNA-seq) across dietary treatment groups, 35 and 10 differentially expressed genes were identified using the and reference annotations, respectively. Maternal overfeeding caused changes in the expression of genes involved in regulating muscle protein synthesis and growth as well as metabolism. Alternately, maternal nutrient restriction affected genes that are involved in muscle cell proliferation and signal transduction. That is, despite a similar phenotype, the genes identified differed between offspring born to restricted- or overfed, ewes indicating that the mechanism for the phenotypic changes in muscle are due to different mechanisms.

The effects of poor maternal nutrition during gestation on postnatal growth and development of lambs.

Poor maternal nutrition can affect the growth and development of offspring, which may lead to negative consequences in adult life. We hypothesized that lambs born to poorly nourished ewes would have reduced growth rate and increased fat deposition, with corresponding changes in the somatotropic axis, and leptin, insulin and glucose concentrations. Ewes ( = 36; 12/treatment) were assigned 1 of 3 diets; 100% (CON), 60% (RES), or 140% (OVER) of NRC requirements for TDN at d 31 of gestation until parturition. One lamb per ewe ( = 35; 11 to 12 per treatment) was used; 18 lambs were euthanized at d 1, and 17 were fed the same diet for 3 mo and then euthanized. Lamb crown rump length (CRL), heart girth, BW, and BCS were measured, and blood samples were collected at d 1 and then at weekly intervals until euthanasia. Averaged from d 1 until 3 mo, lambs from OVER ewes were larger compared with lambs born to CON ewes (BW [16.97 vs. 15.44 kg ± 0.60; = 0.09], ADG [0.23 vs. 0.21 ± 0.01 kg/d; = 0.01], and CRL [68.9 vs. 66.1 ± 0.80 cm; = 0.02]). On a BW basis, heart weight from lambs from RES (0.18 kg ± 0.03; = 0.03) ewes was greater than that of CON lambs (0.15 kg ± 0.03). Backfat thickness was reduced in RES lambs (0.11 ± 0.06; ≤ 0.04) compared with CON (0.20 ± 0.06) and OVER (0.26 ± 0.06) lambs. Concentrations of IGF-I at 3 mo and IGFBP-3 from weaning (d 56 of age) to 3 mo of age tended to be greater ( ≤ 0.06) in OVER lambs (334 ± 66 ng/mL and 175 ± 11 arbitrary units [AU], respectively) than CON lambs (149 ± 66 ng/mL and 140 ± 11 AU, respectively). At 3 mo, leptin was greater in OVER lambs compared with RES lambs (1.24 vs. 0.78 ± 0.13 ng/mL; < 0.05). Over time, average insulin concentrations were greater in OVER and RES lambs than CON lambs (0.49 and 0.49 vs. 0.33 ± 0.05 ng/mL; ≤ 0.02). However, concentrations of GH, IGFBP-2, glucose, triglycerides, and total cholesterol were not different ( > 0.10) between treatment groups. During in vivo glucose tolerance test, baseline insulin concentrations were 68% and 85% greater ( 0.01), respectively, in RES and OVER lambs compared with CON lambs. Similarly, the glucose:insulin ratio was greater in RES and OVER lambs compared with CON lambs ( 0.01). Thus, in this experiment, poor maternal nutrition during gestation influenced body size, organ growth, fat accumulation, and concentrations of IGF-I, IGFBP-3, leptin, and insulin of offspring during the first 3 mo of age.

Restricted maternal nutrition alters myogenic regulatory factor expression in satellite cells of ovine offspring.

Poor maternal nutrition inhibits muscle development and postnatal muscle growth. Satellite cells are myogenic precursor cells that contribute to postnatal muscle growth, and their activity can be evaluated by the expression of several transcription factors. Paired-box (Pax)7 is expressed in quiescent and active satellite cells. MyoD is expressed in activated and proliferating satellite cells and myogenin is expressed in terminally differentiating cells. Disruption in the expression pattern or timing of expression of myogenic regulatory factors negatively affects muscle development and growth. We hypothesized that poor maternal nutrition during gestation would alter the in vitro temporal expression of MyoD and myogenin in satellite cells from offspring at birth and 3 months of age. Ewes were fed 100% or 60% of NRC requirements from day 31±1.3 of gestation. Lambs from control-fed (CON) or restricted-fed (RES) ewes were euthanized within 24 h of birth (birth; n=5) or were fed a control diet until 3 months of age (n=5). Satellite cells isolated from the semitendinosus muscle were used for gene expression analysis or cultured for 24, 48 or 72 h and immunostained for Pax7, MyoD or myogenin. Fusion index was calculated from a subset of cells allowed to differentiate. Compared with CON, temporal expression of MyoD and myogenin was altered in cultured satellite cells isolated from RES lambs at birth. The percent of cells expressing MyoD was greater in RES than CON (P=0.03) after 24 h in culture. After 48 h of culture, there was a greater percent of cells expressing myogenin in RES compared with CON (P0.05). In satellite cells from RES lambs at 3 months of age, the percent of cells expressing MyoD and myogenin were greater than CON after 72 h in culture (P<0.05). Fusion index was reduced in RES lambs at 3 months of age compared with CON (P<0.001). Restricted nutrition during gestation alters the temporal expression of myogenic regulatory factors in satellite cells of the offspring, which may reduce the pool of myoblasts, decrease myoblast fusion and contribute to the poor postnatal muscle growth previously observed in these animals.

Poor maternal nutrition during gestation in sheep reduces circulating concentrations of insulin-like growth factor-I and insulin-like growth factor binding protein-3 in offspring.

To determine if poor maternal nutrition alters growth, body composition, circulating growth factors, and expression of genes involved in the development of muscle and adipose of offspring, 24 Dorset and Shropshire ewes were fed either 100% (control fed), 60% (restricted fed), or 126% (over fed) of National Research Council requirements. Diets began at day 116 ± 6 of gestation until parturition. At parturition, 1 lamb from each control fed (CON), restricted fed (RES), and over fed (OVER) ewe was necropsied within 24 h of birth (1 d; n = 3/treatment) or reared on a control diet for 3 mo (CON = 5, RES = 5, and OVER = 3/treatment) and then euthanized. Body weights and blood samples were collected from lambs from 1 d to 3 mo. Organ weights, back fat thickness, loin eye area, and tissue samples (quadriceps, adipose, and liver) were collected at 1 d and 3 mo of age. The RES lambs weighed 16% less than CON (P = 0.01) between 1 d and 3 mo of age. In RES, there was a tendency for reduced heart girth at 1 d and 3 mo (P < 0.07) and back fat was reduced 36% at 3 mo (P = 0.03). Heart weight was 30% greater in OVER at 1 d when compared with RES lambs (P = 0.02). Serum IGF-I and IGFBP-3 were reduced in RES and OVER lambs (P < 0.05). Leptin tended to be greater in OVER lambs compared with CON at 1 d and 3 mo (P ≤ 0.08). Triiodothyronine was reduced in RES at 1 d (P = 0.05) and triglycerides tended to be greater in OVER at 3 mo (P = 0.07). In liver, there was a tendency for increased expression of IGF-I in OVER (P = 0.06) and decreased IGFBP-3 in RES (P = 0.09) compared with CON lambs at 1 d. In adipose tissue, adiponectin expression was decreased in RES (P = 0.05) at 3 mo. At 1 d of age, muscle expression of IGF-I tended to increase in RES (P = 0.06). In conclusion, poor maternal nutrition during gestation reduced growth rate in offspring which may be because of reduced circulating IGF-I and IGFBP-3 and decreased expression of IGFBP-3 in the liver.

Growth rate and changes of the somatotropic axis in beef cattle administered exogenous bovine somatotropin beginning at two hundred, two hundred fifty, and three hundred days of age.

To determine the effects of bovine somatotropin (bST) treatment beginning at 3 ages on the growth rate and components of the somatotropic axis, 40 beef cattle (200 +/- 21 d of age) were randomly assigned to 1 of 4 treatments (10 animals/treatment). Three of the treatment groups received bST (33 mug/kg of BW) daily beginning at 200, 250, or 300 d of age until all animals reached 400 d of age; the fourth group served as controls (0 bST). Animals were housed in pens (5 animals per pen; 2 pens per treatment) and fed a diet formulated for an ADG of 1.2 kg/d. Feed intake (per pen) was measured daily, and BW was determined weekly. Blood samples (10 mL) and ultrasound measurements were collected at 200, 250, 300, 350, and 400 d of age. Serum concentrations of ST and IGF-I were determined by RIA and IGFBP-2 and -3 by ligand blot procedures. Overall, cattle gained 284.0 +/- 14.7 kg of BW with a treatment x week interaction (P < 0.01), such that during the treatment period ADG was 11.6, 8.7, and 15.8% greater (P < 0.05) in cattle treated with bST beginning at 200, 250, and 300 d, respectively, relative to controls during the same time frame. Average DMI was 13.6% less (P < 0.05) in bST-treated cattle than in controls. Increases in ADG coupled with a reduction in DMI resulted in 11.7, 14.0, and 26.4% increases (P < 0.01) in the efficiency of gain (G:F) in bST-treated cattle beginning at 200, 250, and 300 d of age, respectively, compared with contemporary controls. Backfat thickness increased (P < 0.05) over time, but the magnitude of the increase was less in the bST-treated cattle (treatment x week interaction; P < 0.05). Area of the LM increased (P < 0.05) over time but was similar across treatment groups. Serum concentrations of ST, IGF-I, and IGFBP-3 increased (P < 0.05), whereas IGFBP-2 decreased (P < 0.05) over time. The changes in the components of somatotropic axis were more pronounced in bST-treated cattle compared with controls, with the greatest magnitude of response in animals that began bST treatment at 300 d of age. In conclusion, the exogenous bST-induced growth response was greater in animals that began to receive bST administration at 300 d of age and received it for a shorter period (100 d) compared with animals that received bST beginning at 200 or 250 d of age.

Growth hormone response to growth hormone releasing hormone in calves that differ in genetic merit for milk yield.

Holstein heifer, steer, and bull calves from control (CL) and select (SL) lines of cows that differed by more than 4000 kg of milk during a 305-d lactation (SL > CL) were used to determine growth hormone (GH) response to 5 doses of GH releasing hormone (GHRH) and how this response was affected by gender, period (age), and genetic merit for milk yield. Doses (0, 2.5, 5, 10, and 20 microg/100 kg of BW) of a GHRH analog were assigned randomly to each heifer (4 CL, 4 SL), steer (4 CL, 4 SL), and bull (3 CL, 3 SL) calf and administered on consecutive days at approximately 3, 6, and 10 mo of age (periods; P1, P2, and P3). Jugular blood samples (n = 15) collected between -30 and 240 min relative to GHRH administration were used to quantify area under the GH response curve (AUC) after subtracting mean prechallenge GH concentrations. Estimates of maximum response (Rmax) and sensitivity (ED50) to GHRH were obtained from the hyperbolic dose response curves (AUC vs. dose). Data were analyzed for effects of dose, line, period, gender, and their interactions with period as the repeated effect. Prechallenge GH concentrations were not affected by genetic line, gender, or period. The AUC was not affected by line, but decreased with period and increased with GHRH dose. The Rmax did not differ between lines or among genders, but decreased with period. The ED50 did not differ between lines or among periods, but heifers were more sensitive to GHRH than steers or bulls. Although GH response to GHRH has been identified as a potential indicator of genetic merit, it did not differ between these substantially different genetic lines.

The ontogeny of the somatotropic axis in Hereford calves from birth to one year of age and its response to administration of exogenous bovine somatotropin.

Administration of exogenous bovine ST (bST) increases growth rate, feed efficiency, and carcass quality in beef cattle. The magnitude of response to bST in beef cattle is variable and related to the age of the animal. Our objective was to determine the response of the somatotropic axis, in particular IGF-I, IGFBP-2, and IGFBP-3, to bST treatment from birth to 1 yr of age. Blood samples were collected before and after a single injection of bST (500 mg) every 50 d from birth to 1 yr of age in male and female Hereford calves. Body weights and serum concentrations of ST, IGF-I, IGFBP-2, and IGFBP-3 were determined. At birth, serum concentrations of ST, IGF-I, and IGFBP-3 increased (P < 0.05) following bST treatment. From 50 to 350 d of age, average concentrations of ST and IGF-I were greater (P < 0.05) in males, whereas IGFBP-2 concentrations were greater (P < 0.05) in females. No gender differences in IGFBP-3 concentrations were observed. Following bST treatment, IGF-I increased (P < 0.05) from 50 to 350 d of age, IGFBP-2 decreased (P < 0.05) from 50 to 200 d of age, and IGFBP-3 increased (P < 0.05) at 250 d of age. At 250 d of age, baseline concentrations of IGFBP-2 decreased (P < 0.05). Due to the positive response of IGFBP-3 and decreased baseline IGFBP-2 at 250 d of age, we conclude that this is an age at which the somatotropic axis is most responsive to exogenous bST, and it therefore may be an appropriate age to begin bST treatment in beef calves to realize the positive influence of bST on BW gain, feed efficiency, and carcass composition.

The ontogeny of the somatotropic axis in male and female Hereford calves from birth to one year of age.

Insulin-like growth factor-binding proteins-2 and -3 may play a role in age-dependent growth response to bovine ST (bST) treatment in cattle; however, samples have been collected at infrequent intervals and at limited time points. Therefore, the objective of this experiment was to examine the ontogeny of components of the somatotropic axis in Hereford calves from birth to 1 yr of age at weekly intervals to determine whether there is a certain age or time frame when the somatotropic axis may change and/or potentially become more responsive to exogenous bST administration. Blood samples and body weight measurements were collected from eight male and eight female Hereford calves once per week from birth to 1 yr of age. Serum concentrations of ST, IGF-I, IGFBP-2, and IGFBP-3 were determined. Males began to grow faster than females at approximately 16 wk of age (P < 0.05). Average concentrations of ST, IGF-I, and IGFBP-3 were greater in males than females (P < 0.01). Average concentrations of IGFBP-2 were greater in females than in males (P = 0.05). Concentrations of ST decrease with age (P < 0.01); however, the decrease occurred earlier in female calves. Concentrations of IGF-I and IGFBP-3 increased in males and females (P < 0.01), and concentrations of IGF-I began to plateau at approximately the same time as growth rate differences were observed (16 wk of age). Following an initial increase (birth to approximately 16 wk of age), concentrations of IGFBP-3 remained constant until approximately 43 wk of age. Concentrations of IGFBP-2 increased to approximately 10 wk of age (P < 0.05), followed by a decrease, and then, similar to IGFBP-3, remained constant until 43 wk of age. Correlations between average daily gain, ST, IGF-I, IGFBP-2, and IGFBP-3 were determined. Average daily gain was negatively (P < 0.01) correlated with ST and positively (P < 0.1) correlated with IGF-I. In females, ST was negatively (P < 0.01) correlated with IGF-I. Concentrations of ST were positively correlated (P < 0.01) with IGFBP-2 and IGFBP-3. Concentrations of IGFBP-2 were negatively correlated (P < 0.01) with IGF-I and positively correlated (P < 0.01) with IGFBP-3. In conclusion, serum concentrations of ST, IGF-I, IGFBP-2, and IGFBP-3 differed between male and fe-male calves. In addition, changes in components of the somatotropic axis occurred around the same time as males began to grow faster than females.

Effects of selection for milk yield on growth hormone response to growth hormone releasing factor in growing Holstein calves.

Bull and heifer calves (n = 81) from genetic lines of Holstein cows that differed by more than 4000 kg milk/305-d lactation were used to determine effects of selection for milk yield on growth hormone (GH) response to a GH releasing factor (GRF) analog. Calves received GRF (4 microg/100 kg BW) on 10, 56, 140, 196, 252, and 364 +/- 3 d of age. Jugular blood samples (n = 15) were obtained from -30 to 120 min relative to GRF administration. Area under the GH response curve (0 to 60 min, AUC60) was quantified after subtracting mean prechallenge GH concentrations. Data were analyzed for effects of line, age, gender, and their interactions with PROC MIXED of SAS for repeated measures and incorporated the spatial power law for unequally spaced data with age as the repeated effect. Means were considered different when P < 0.05. Prechallenge GH concentrations did not differ between lines, were greater in bulls than heifers (4.6 vs. 3.7 ng/ml), and decreased with age. The AUC60 decreased with age but did not differ between lines. Heifers responded more to GRF than bulls (1550 vs. 1336 ng x min/ml). Peak GH concentration decreased with age and was less in bulls than heifers (54.7 vs. 62.1 ng/ml) but did not differ between lines. Although plasma GH has been identified as an inheritable trait, we conclude the GH variables measured in this study were not useful in predicting genetic merit of calves from these substantially different lines of cows.

The influence of level of feeding on growth and serum insulin-like growth factor I and insulin-like growth factor-binding proteins in growing beef cattle supplemented with somatotropin.

The objective of this study was to determine the effects of level of feeding on growth, feed efficiency (gain:feed; G:F), body composition (BC), and serum concentrations of somatotropin (ST), IGF-I, and IGF-binding proteins (BP) in growing beef cattle supplemented with bovine (b) ST. In each of two consecutive years, 40 growing beef cattle were blocked by weight (average BW: yr 1 = 316 kg, yr 2 = 305 kg) and used in a 2 x 2 factorial arrangement with main effects of bST (0 or 33 microg x kg BW(-1) x d(-1)) and level of feed intake (ad libitum [AL] or 0.75 AL). Relative to uninjected cattle, treatment with bST increased ADG 9.6% (1.14 vs 1.25 kg/d; P < 0.05) and increased G:F 8.1% (12.3 vs 13.3 gain [g]:feed [kg]; P < 0.05), whereas ADG in AL animals was 39% greater than that in 0.75 AL animals (1.39 vs 1.00 kg/d; P < 0.05). There was a tendency (P = 0.10) for a bST x level of feeding interaction, such that the increase in ADG with bST was greater in AL cattle than in 0.75 AL cattle (10.6 vs 7.8%; P = 0.10). Serum concentrations of ST were greater in 0.75 AL cattle than in AL cattle (13.0 vs 8.6 ng/mL; P < 0.05) and in bST-treated cattle than in uninjected cattle (16.3 vs 5.2 ng/mL; P < 0.05). Due to a bST x level of feeding interaction (P < 0.01), the magnitude of the increase in serum ST to exogenous bST was greater (P < 0.01) in 0.75 AL cattle than in AL cattle. Relative to uninjected cattle, treatment with bST increased (P < 0.05) serum concentrations of IGF-I and IGFBP-3 and reduced (P < 0.05) concentrations of IGFBP-2. Similarly, AL cattle had greater (P < 0.05) serum concentrations of IGF-I and IGFBP-3 and reduced (P < 0.05) IGFBP-2 compared with 0.75 AL cattle. In summary, treatment with bST increased growth rate and G:F and stimulated serum IGF-I and IGFBP-3 while reducing IGFBP-2. Feeding at 0.75 ad libitum intake reduced the magnitude of response for each of these variables. Thus, limit-feeding may reduce the effect of exogenous bST on growth rate by blunting bST-induced increases in IGF-I and IGFBP-3 and bST-induced decreases in IGFBP-2.

Body composition and estimated tissue energy balance in Jersey and Holstein cows during early lactation.

The rate and extent of estimated energy mobilization and the relationship between fat depth at the rib and thurl and body condition score (BCS) were investigated in Jersey and Holstein cows in early lactation. Twenty-six cows were paired by breed, parity, and calving date, and were individually fed a total mixed ration ad libitum from parturition through 120 d in milk. Feed intake and milk production were measured daily; body weight (BW), BCS, subcutaneous fat depth, milk composition, and concentration of plasma nonesterified fatty acids were measured every 2 wk. Estimated tissue energy balance (TEB) was calculated using 1989 NRC equations. Net energy intake was greater in early lactation for Holsteins compared with Jerseys, 37.8 and 28.2 Mcal/d, respectively. Milk energy was greater for Holsteins relative to Jerseys, 30.5 versus 21.2 Mcal/d. Fat depth and BCS did not differ between breeds. A positive relationship existed between fat depth and BCS for Jerseys; however, there was no significant relationship for Holsteins. The best-fit regression model for predicting TEB for Holsteins and Jerseys in early lactation included week of lactation, milk composition, and BCS. Jerseys remained in negative TEB for a shorter period of time relative to Holsteins. The TEB nadir was -6.19 and -12.9 Mcal/d, for Jerseys and Holsteins, respectively. Expressed as a proportion of metabolic BW (BW(0.75)), net energy intake did not differ between breeds, yet milk energy and estimated tissue energy loss were greater for Holsteins compared with Jerseys.

Actions and interactions of thyroid hormone and zinc status in growing rats.

Both thyroid hormone (triiodo-L-thyronine, T3) and zinc play important roles in growth and development. The T3 receptor is thought to require zinc to adopt its biologically active conformation. Some of the effects of zinc deficiency, therefore, may be due to loss of zinc from the T3 receptor and impairment of T3 action. This possibility was investigated in growing rats by examining the effects of hypothyroidism and hyperthyroidism in zinc-deficient, pair-fed and control rats. Measurement of serum zinc and T3 confirmed the efficacy of the treatments. Zinc deficiency and hypothyroidism resulted in lower food intake and growth failure, but no interaction was observed between the two treatments. Individual tissue weights were influenced by thyroid status as expected, regardless of zinc status. Both dietary and hormonal treatments influenced serum insulin-like growth factor (IGF)-I in an interactive manner. IGF-I was reduced to a greater extent in zinc-deficient than in pair-fed rats compared with controls. Both hypothyroidism and hyperthyroidism reduced serum IGF-I, and a greater reduction due to hyperthyroidism was apparent in zinc-deficient rats. IGF binding proteins were also influenced by diet and thyroid status. The hepatic expression of mRNA S14 was assessed as a direct index of the nuclear action of T3, but its response was not influenced by dietary treatment. Although confirming the role of both T3 and zinc in the regulation of growth and the somatotrophic axis, the growth failure of zinc deficiency does not appear to be due to impaired T3 function.