Transition milk stimulates intestinal development of neonatal Holstein calves.

Colostrum stimulates gastrointestinal development. Similar to colostrum, transition milk (TM; the first few milkings after colostrum) contains elevated nutrient levels and bioactive components not found in milk replacer (MR), albeit at lower levels than the first colostrum. We hypothesized that feeding neonatal calves TM, compared with MR, for 4 d following colostrum at birth would further stimulate intestinal development. Holstein bull calves were fed 2.8 L of colostrum within 20 min of birth, allocated to 1 of 11 blocks based on birth date and body weight (BW), randomly assigned to MR (n = 12) or TM (n = 11) treatments within block, and fed treatments 3 times per day. Milk from milkings 2, 3, and 4 (TM) of cows milked 2 times daily was pooled by milking number and fed at 1.89 L per feeding; milking 2 was fed at feedings 2 through 5, milking 3 at feedings 6 through 8, and milking 4 at feedings 9 through 12. TM was not pasteurized and contained 17% solids, 5% fat, 7% protein, 4% lactose, and 20 g of IgG per liter on average, whereas MR (as fed) contained 15% solids, 4% protein, 3% fat, 6% carbohydrate, and no IgG. Refusals were similar, so calves fed TM consumed 1.0 Mcal of metabolizable energy per day more than those fed MR. On the morning of d 5, calves were injected i.v. with 5 mg of bromodeoxyuridine per kg of BW and slaughtered 130 min later; then, intestinal sections were excised. Feeding TM, instead of MR, doubled villus length, villus width, villus to crypt ratio, and mucosal length in all intestinal sections, increased submucosal thickness 70% in the proximal and mid jejunum, and tended to increase submucosal thickness in duodenum and ileum. Mucosal surface area was also increased in both the ileum and mid jejunum when feeding TM by 19 and 36%, respectively. Treatment did not alter crypt depth. Bromodeoxyuridine labeling was increased 50% by TM compared with MR in the cells along the epithelium of the crypts and within the villi of all sections, indicating that TM increased cell proliferation compared with MR. Calves fed TM gained more BW than calves fed MR and had improved cough, fecal, nose, and ear scores. We conclude that feeding TM for 4 d following an initial feeding of colostrum stimulates villus, mucosal, and submucosal development in all sections of the small intestine in the first few days of life and improves health and growth.

Anti-Müllerian Hormone (AMH) and fertility management in agricultural species.

A reliable, easy to assess marker for fertility in agricultural species would be highly desirable and Anti-Müllerian Hormone (AMH) is a promising candidate. This review summarizes recent findings concerning AMH and its role in fertility management, mainly in cattle. It focuses on (1) alterations in circulating AMH concentrations from birth to puberty and during estrous cycles; (2) correlation of circulating AMH concentrations with ovarian follicle numbers and ovarian reserve; (3) factors that impact circulating AMH concentrations; (4) use of AMH as a predictor of fertility. Circulating AMH concentrations can be easily and reliably measured with a single blood sample in adult cattle because AMH varies minimally during the estrous cycle and is repeatable across multiple cycles. Circulating AMH concentrations are positively associated with several measures of fertility. Dairy heifers with low compared with higher AMH concentrations subsequently had lower pregnancy rates, higher probability of being culled after birth of their first calf and shorter herd longevity. Also, AMH is predictive of response to superovulation in cattle and sheep. Several factors contribute to the variability in AMH concentrations among individuals; for example, beef cattle have higher AMH than dairy cattle. Nutritional imbalances, disease and endocrine disruptors during fetal life may negatively program the size of the ovarian reserve and consequently serum AMH concentrations and potential fertility in adulthood. We conclude that AMH may be a predictor of fertility and herd longevity in cattle, whereas in sheep and other farm species, the potential association between AMH and reproductive performance remains largely unexplored.Free Italian abstract: An Italian translation of this abstract is freely available at http://www.reproduction-online.org/content/154/1/R1/suppl/DC1.

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 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.

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.

Use of an immortalized bovine mammary epithelial cell line (MAC-T) to measure the mitogenic activity of extracts from heifer mammary tissue: effects of nutrition and ovariectomy.

The objectives of the experiment were (1) to determine whether MAC-T cells would accurately mimic the previously observed proliferative responses of primary mammary epithelial cells (MEC) to mammary tissue extracts from high and low-fed heifers and (2) to determine whether mammary tissue extracts from ovariectomized (OVX) heifers would have lower mitogenic activity than intact controls. Addition of mammary tissue extracts to cell culture media of MAC-T cells plated on plastic or collagen-coated plastic to a range of concentrations between 1 and 8% resulted in dose-dependent increases in cell proliferation. Furthermore, mammary tissue extracts from low-fed prepubertal heifers aged 9 months, stimulated significantly more proliferation of MAC-T cells, as measured by 3H-thymidine incorporation into DNA than mammary tissue extracts from high-fed heifers (40.6 cpm x 10(3) per well versus 21.9+/-1.8 cpm x 10(3) per well). These observations suggested that MAC-T cells would be a suitable alternative to primary MECs for measuring the mitogenic activity of mammary tissue extracts. Conversely, no difference was observed in the mitogenic activity of mammary tissue extracts from OVX or control heifers. Possibly, MAC-T cells provide a good model for nutrition- but not ovarian-induced changes in mammary growth. Alternatively, that reduction of in vivo mammary development following OVX did not result in reduced mitogenic activity of the mammary tissue extracts emphasizes that heifer mammary development is the result of complex interactions between local growth factors and systemic hormones.

A partnership of universities and agri-business for an effective dairy herd management learning experience for undergraduates: the Dairy Challenge.

The Dairy Challenge contest allows undergraduate students to apply knowledge gained in the classroom in an evaluation of the management practices of commercial dairy farms. University faculty partnered with industry representatives to develop the competition. Participants in the Dairy Challenge do the following: 1) critically evaluate dairy herd management practices and make recommendations for improvements; 2) visit local dairy farms and gain knowledge of different farms' management practices; 3) meet and interact with potential employers from the dairy industry during the contest; 4) evaluate herd records and utilize knowledge of dairy herd management software and computer presentation tools; 5) test their speaking, presentation, and problem-solving skills; and 6) work as a team to build consensus and tag-team speaking formats. Teams of four undergraduate students critically evaluate a commercial dairy farm using herd records, a description of farm operations, and tour of the farm facilities. The farmer answers questions pertaining to management of the farm in a group interview with all teams and in a separate interview with each individual team. Teams give a 20-min presentation that is scored on the description and assessment of the management practices and recommendations for improvements in management and facilities. Additionally, scoring is based on apparent level of preparation, speaking, presentation skills, and responses to judges' questions. The judges are university specialists and dairy industry professionals. This capstone experience allows students to interact with dairy farmers and representatives from the dairy industry and expands their knowledge and skills gained during their academic career.

Evidence for a local effect of leptin in bovine mammary gland.

On average, high-energy diets promoting body growth rates above 1 kg/d before puberty impair mammary development by 15 to 20% in cattle. We hypothesized that leptin, a protein produced by adipocytes, mediates the inhibitory effect of high-energy diets on mammary development. Therefore, our objectives were to determine the effect of leptin on mammary epithelial cell proliferation, and the distribution of mRNA for two leptin receptor isoforms in prepubertal bovine mammary glands and other peripheral tissues. Addition of leptin to culture media containing either 5 ng/ml of insulin-like growth factor-I (IGF-I) or 1% fetal bovine serum decreased DNA synthesis of a bovine mammary epithelial cell line (MAC-T) in a dose-dependent manner. The minimal doses of leptin that decreased IGF-I- and fetal bovine serum-stimulated cell proliferation were 64 and 1 ng/ml, respectively. In addition, we determined that MAC-T cells and isolated bovine mammary epithelial cells express the long form of leptin receptor (Ob-Rb) mRNA. Ob-Rb mRNA was detected in all bovine tissues examined. In contrast with reports on other species, mRNA expression of the short form of leptin receptor (Ob-Ra) was detected only in bovine liver, pituitary body, and spleen. These results support the concept that leptin mediates the inhibitory effect of high-energy diets on mammary development.