L.T. Chapin

Effect of intensified feeding of heifer calves on growth, pubertal age, calving age, milk yield, and economics

The objective of this study was to determine if increasing the energy and protein intake of heifer calves would affect growth rates, age at puberty, age at calving, and first lactation milk yield. A second objective was to perform an economic analysis of this feeding program using feed costs, number of nonproductive days, and milk yield data. Holstein heifer calves born at the Michigan State Dairy Cattle Teaching and Research Center were randomly assigned to 1 of 2 dietary treatments (n=40/treatment) that continued from 2 d of age until weaning at 42 d of age. The conventional diet consisted of a standard milk replacer [21.5% crude protein (CP), 21.5% fat] fed at 1.2% of body weight (BW) on a dry matter basis and starter grain (19.9% CP) to attain 0.45 kg of daily gain. The intensive diet consisted of a high-protein milk replacer (30.6% CP, 16.1% fat) fed at 2.1% of BW on a dry matter basis and starter grain (24.3% CP) to achieve 0.68 kg of daily gain. Calves were gradually weaned from milk replacer by decreasing the amount offered for 5 and 12 d before weaning for the conventional and intensive diets, respectively. All calves were completely weaned at 42 d of age and kept in hutches to monitor individual starter consumption in the early postweaning period. Starting from 8 wk of age, heifers on both treatments were fed and managed similarly for the duration of the study. Body weight and skeletal measurements were taken weekly until 8 wk of age, and once every 4 wk thereafter until calving. Calves consuming the intensive diet were heavier, taller, and wider at weaning. The difference in withers height and hip width was carried over into the early post-weaning period, but a BW difference was no longer evident by 12 wk of age. Calves fed the intensive diet were younger and lighter at the onset of puberty. Heifers fed the high-energy and protein diet were 15 d younger at conception and 14 d younger at calving than heifers fed the conventional diet. Body weight after calving, daily gain during gestation, withers height at calving, body condition score at calving, calving difficulty score, and calf BW were not different. Energy-corrected, age-uncorrected 305-d milk yield was not different, averaging 9,778 kg and 10,069 kg for heifers fed the conventional and intensive diets, respectively. However, removing genetic variation in milk using parent average values as a covariate resulted in a tendency for greater milk from heifers fed the intensive diet. Preweaning costs were higher for heifers fed the intensive diet. However, total costs measured through first lactation were not different. Intensified feeding of calves can be used to decrease age at first calving without negatively affecting milk yield or economics.

Effects of Feeding Prepubertal Heifers a High-Energy Diet for Three, Six, or Twelve Weeks on Mammary Growth and Composition

The experimental objective was to determine the effects of feeding prepubertal dairy heifers a high-energy diet for 3, 6, or 12 wk on mammary growth and composition. Holstein heifers (age = 11 wk; body weight = 107 +/- 1 kg) were assigned to 1 of 4 treatments (n = 16/ treatment). The treatment period lasted 12 wk and treatments were H0 (low-energy diet fed for 12 wk, with no weeks on the high-energy diet); H3 (low-energy diet fed for 9 wk, followed by the high-energy diet for 3 wk); H6 (low-energy diet fed for 6 wk, followed by the high-energy diet for 6 wk); and H12 (high-energy diet for all 12 wk). The low- and high-energy diets were formulated to achieve 0.6 and 1.2 kg of average daily gain, respectively. Heifers were slaughtered at 23 wk of age and mammary tissue was collected. A longer duration of feeding the high-energy diet increased total mass of the mammary gland, extraparenchymal fat, and intraparenchymal fat, but did not alter the mass of fat-free parenchymal tissue. When adjusted for carcass weight to reflect differences in physical maturity, the mass of fat-free parenchymal tissue decreased in a linear fashion with a longer duration on the high-energy diet. Total masses of mammary parenchymal DNA and RNA were not different. However, after adjustment for carcass weight, the masses of DNA and RNA decreased as heifers were fed the high-energy diet for a longer duration. The percentages of epithelium, stroma, and lumen, the number of epithelial structures, and the developmental scores of mammary parenchymal tissue were not different among treatments. However, the percentage of proliferating epithelial cells in the terminal ductal units, as indicated by Ki-67 labeling, decreased as heifers were fed the high-energy diet for a longer duration. We concluded that feeding prepubertal heifers a high-energy diet for a longer duration resulted in a linear decrease in both the percentage of mammary epithelial cells that were proliferating and in the mass of fat-free mammary parenchyma per unit of carcass. High-energy feeding hastens puberty and, in this study, decreased mammary epithelial cell proliferation in areas of active ductal expansion. These data are consistent with the idea that feeding heifers a high-energy diet will reduce mammary parenchymal mass at puberty.

Growth Hormone Response of Bull Calves to Growth Hormone-Releasing Factor

Abstract Three experiments were conducted to determine serum growth hormone (GH) response of bull calves (N = 4; 83 kg body wt) to iv injections and infusions of human pancreatic GH-releasing factor 1-40-OH (hpGRF). Peak GH responses to 0, 2.5, 10, and 40 μg hpGRF/100 kg body wt were 7 ± 3, 8 ± 3, 18 ± 7, and 107 ± 55 (mean peak height ± SEM) ng/ml serum, respectively. Only the response to the 40-μg dose was greater (P < 0.05) than the 0-μg dose. Concentrations of prolactin in serum were not affected by hpGRF treatment. In calves injected with hpGRF (20 μg/100 kg body wt) at 6-hr intervals for 48 hr, GH increased from a mean preinjection value of 3.1 ng/ml serum to a mean peak response value of 70 ng/ml serum. Differences in peak GH response between times of injection existed within individual calves (e.g., 10.5 ng/ml vs 184.5 ng/ml serum). Concentrations of GH in calves infused continuously with either 0 or 200 μg hpGRF/hr for 6 hr averaged 7.4 ± 3 and 36.5 ± 11 ng/ml serum, respectively (P < 0.05). Concentrations of GH oscillated markedly in hpGRF-infused calves, but oscillations were asynchronous among calves. We conclude that GH response of bull calves to hpGRF is dose dependent and that repeated injections or continuous infusions of hpGRF elicit GH release, although magnitude of response varies considerably. We hypothesize that differences in GH response to hpGRF within and among calves, and pulsatile secretion in the face of hpGRF infusion may be related to the degree of synchrony among exogenous hpGRF and endogenous GRF and somatostatin.

Effects of Feeding Prepubertal Heifers a High-Energy Diet for Three, Six, or Twelve Weeks on Feed Intake, Body Growth, and Fat Deposition

The objective was to determine the effects of feeding prepubertal dairy heifers a high-energy diet for a duration of 0, 3, 6, or 12 wk on feed intake, growth, and fat deposition. We also used feed composition, daily intake, and body growth data to evaluate the nutritional model of the 2001 National Research Council (NRC) Nutrient Requirements of Dairy Cattle. Holstein heifers (age = 11 wk; body weight = 107 +/- 1 kg) were assigned to 1 of 4 treatments (n = 16/treatment) designated H0, H3, H6, and H12 and fed a low-energy diet for 12, 9, 6, or 0 wk, followed by a high-energy diet for 0, 3, 6, or 12 wk, respectively. Four heifers were killed initially (11 wk of age) and 64 heifers were killed at the end of the treatment period (23 wk of age). The low-energy diet was formulated to achieve 0.6 kg of average daily gain and contained 16% crude protein, and 45% neutral detergent fiber. The high-energy diet was formulated to achieve an average daily gain of 1.2 kg and contained 18% crude protein and 23% neutral detergent fiber. Actual daily gains averaged over the 12-wk treatment period were 0.64, 0.65, 0.83, and 1.09 kg for the H0, H3, H6, and H12 groups, respectively. Body weight, withers height, hip width, carcass weight, liver weight, and perirenal fat increased in heifers fed a high-energy diet for a longer duration. In addition, percentage of fat increased and percentage of protein decreased in rib sections with a longer duration on the high-energy diet. Uterine and ovarian weights adjusted for body weight decreased when heifers were fed the high-energy diet for a longer duration. The 2001 NRC underestimated dry matter intake of the high-energy diet and overestimated dry matter intake of the low-energy diet. On the basis of actual intakes of each diet, the NRC slightly underestimated gain for the low-energy diet and overestimated gain by 40% for the high-energy diet. The likely explanation for this is that the NRC underestimated the proportion of gain that was fat in the heifers fed the high-energy diet and therefore predicted more body gain per unit of energy intake. We concluded that feeding a high-energy diet for a short duration altered body growth and fat deposition in a time-dependent, linear manner consistent with feeding a high-energy diet for a long duration.

α2-Adrenergic Receptor-Mediated Regulation of Growth Hormone Secretion in Meal-Fed Holstein Steers

Abstract Effects of activation or blockade of α2-adrenergic receptors on serum growth hormone concentrations were studied in Holstein steers (115 ± 4 days of age; 112 ± 4 kg body wt). A pelleted diet was available ad libitum for 2 hr each day. Serum growth hormone concentrations were greater for 80 min immediately before feeding compared with 80 min immediately after removal of feed. Relative to saline-injected controls, activation of α2-adrenergic receptors with clonidine (2 μg/kg body wt iv) before feeding rapidly increased serum growth hormone concentrations, but clonidine had no effect when administered after feeding. Compared with vehicle-injected controls, blockade of α2-adrenergic receptors with either idazoxan (20 mg/kg body wt sc) or yohimbine (5 mg/kg body wt sc) decreased serum growth hormone concentrations before as well as after feeding. Feeding abolished the stimulatory α2-adrenergic receptor-mediated increase in growth hormone secretion. Our data support the hypothesis that α2-adrenergic receptor stimulation is an essential event mediating pulsatility of growth hormone secretion before feeding and is required to maintain basal concentrations after feeding.

Temperature effects on serum prolactin concentrations and activity of dopaminergic neurons in the infundibulum/pituitary stalk of calves

Abstract The effects of ambient temperature on serum concentrations of prolactin and neurochemical estimates of activity of dopaminergic neurons projecting to the infundib-ulum/pituitary stalk were investigated in Holstein bull calves. Accumulation of 3,4-dihydroxyphenylalanine (DOPA) in the infundibulum/pituitary stalk after intravenous injection of a decarboxylase inhibitor was used to estimate activity of these dopaminergic neurons. Increasing ambient temperature from 21 to 33°C for 22 hr increased serum concentrations of prolactin and decreased activity of the dopaminergic neurons. Conversely, reducing ambient temperature from 22°C to 11°C decreased serum concentrations of prolactin and increased activity of these dopaminergic neruons. It is suggested that alterations in activity of dopaminergic neurons terminating in the infundibulum/pituitary stalk of bull calves may mediate acute temperature-induced changes in secretion of prolactin.

Pituitary adenylate cyclase-activating polypeptide induces secretion of growth hormone in cattle.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a hypothalamic neuropeptide that stimulates release of growth hormone (GH) from cultured bovine anterior pituitary gland cells, but the role of PACAP on the regulation of in vivo secretion of GH in cattle is not known. To test the hypothesis that PACAP induces secretion of GH in cattle, meal-fed Holstein steers were injected with incremental doses of PACAP (0, 0.1, 0.3, 1, 3, and 10 microg/kg BW) before feeding and concentrations of GH in serum were quantified. Compared with saline, injection of 3 and 10 microg PACAP/kg BW increased peak concentrations of GH in serum from 11.2 ng/ml to 23.7 and 21.8 ng/ml, respectively (P < 0.01). Peak concentrations of GH in serum were similar in steers injected with 3 or 10 microg PACAP/kg BW. Meal-fed Holstein steers were then injected with 3 microg/PACAP/kg BW either 1 hr before feeding or 1 hr after feeding to determine if PACAP-induced secretion of GH was suppressed after feeding. Feeding suppressed basal concentrations of GH in serum. Injection of PACAP before feeding induced greater peak concentrations of GH in serum (19.2 +/- 2.6 vs. 11.7 +/- 2.6 ng/ml) and area under the response curve (391 +/- 47 vs. 255 +/- 52 ng. ml(-1) min) than injection of PACAP after feeding, suggesting somatotropes become refractory to PACAP after feeding similar to that observed by us and others with growth hormone-releasing hormone (GHRH). We concluded that PACAP induces secretion of GH and could play a role in regulating endogenous secretion of GH in cattle, perhaps in concert with GHRH.

Stimulation of Dopamine D1 Receptors Increases Activity of Periventricular Somatostatin Neurons and Suppresses Concentrations of Growth Hormone

The selective dopamine D1 receptor agonist, SKF38393, stimulates release of somatostatin (SS) from perifused bovine hypothalamic slices. Therefore, we hypothesized that SKF38393 activates SS neurons, which, via release of SS, would suppress concentrations of growth hormone (GH) in serum in calves. Our objectives were to determine whether SKF38393: (1) increases the percent of immunoreactive c-Fos protein and Fos-related antigens (Fos/FRA) detected in somatostatin neurons in periventricular (PeVN) and arcuate (ARC) hypothalamic nuclei; (2) reduces concentrations of GH in serum; (3) suppresses growth hormone-releasing hormone (GHRH)-induced release of GH. Meal-fed steers were used to perform these objectives because a synchronous pulse of GH occurs 1-2 hr before feeding in steers allowed access to feed for 2 hr each day. In Experiment 1, two groups of four Holstein steers were injected s.c. with either vehicle (sterile water) or SKF38393 (5 mg/kg BW). Steers were injected i.v. with a lethal dose of sodium pentobarbital 100 min later and their brains were fixed with 4% paraformaldehyde. Dual-label immunohistochemistry was performed on 40 microns free-floating sections using antiserum to SS and to Fos/FRA on sections containing PeVN and ARC nuclei. More SS neurons were detected in the PeVN than in the ARC. The percent of SS neurons with immunoreactive Fos/FRA present was 2.9-fold higher in SKF38393-treated compared with vehicle-injected steers in the PeVN, but was unchanged in the ARC. In Experiment 2, eight Holstein steers were injected s.c. with either vehicle (sterile water) or SKF38393 (5 mg/kg BW) 140 min before meal-feeding. In contrast to controls, concentrations of GH in serum of SKF38393-treated steers did not increase during 140 min before meal-feeding. In Experiment 3, eight Holstein steers were injected s.c. with either vehicle (sterile water) or SKF38393 (5 mg/kg BW), then 100 min later, each steer was injected i.v. with [Leu27,Hse45] bGHRH1-45 lactone (0.2 micrograms/kg BW). Bovine GHRH stimulated release GH into serum in both groups, but concentrations of GH were lower in SKF38393-treated steers. These results show that stimulation of D1 receptors selectively increases activity of SS neurons in the PeVN, and this increased activity is associated with suppressed basal- and GHRH-induced release of GH in serum of meal-fed steers.

Prolonged suppression of serum concentrations of melatonin in prepubertal heifers

Abstract: Our objective was to suppress the daily surge of melatonin in serum of prepubertal dairy heifers by manipulating intensity of light (Experiment 1) and duration of exposure to light (Experiment 2). Heifers in Experiment 1 were exposed to either 12 hr of darkness (000 lux, control), or 400, 800, or 1,200 lux of light during the last 6 hr of their usual 12‐hr nocturnal period. During this 6‐hr exposure to various intensities of light, melatonin concentrations were similar to their respective daytime baseline values measured under 400 lux of light, but were 62% to 82% lower than melatonin concentrations during their nocturnal surge period. Suppression of melatonin concentrations was similar between 400 and 1,200 lux of light. In Experiment 2, heifers were exposed to LD 8:16, LD 16:8, LD 20:4, or LD 24:0 photoperiods (1,200 lux) for 4 months. Throughout treatment, concentrations and durations of the melatonin surge were suppressed in the LD 24:0 group and were greatest (during the nocturnal period) in the LD 8:16 group. Concentrations of prolactin in serum were elevated in animals under long days relative to LD 8:16 treatment and respective pretreatment periods. In conclusion, continuous light at an intensity of 1,200 lux suppressed the nocturnal surge of melatonin, but increased secretion of prolactin for at least 4 months in prepubertal heifers.

The Effect of Lamps with Different Spectral Properties on Prolactin Release in Prepubertal Bulls

Abstract Concentrations of prolactin in serum increased 1.8- to 7.8-fold within 6 weeks after duration of daily light was shifted from 8 to 16 hr. In comparison with cool-white fluorescent light, this increment in concentration of prolactin was similar when a light source that simulates natural sunlight (Vita-Lite), or incandescent, high-pressure sodium, or mercury vapor lamps were used. Regardless of light source, increasing the duration of daily light from 8 to 16 hr during warmer months (Aug) resulted in a greater magnitude of increase in mean prolactin concentrations as compared with increases observed during cooler months (Feb). We conclude that in prepubertal bulls, secretion of prolactin increases similarly when duration of light from lamps with different spectral properties is increased from 8 to 16 hr daily.