Production of a gonadotropin-releasing hormone 2 receptor knockdown (GNRHR2 KD) swine line.

Swine are the only livestock species that produce both the second mammalian isoform of gonadotropin-releasing hormone (GNRH2) and its receptor (GNRHR2). Previously, we reported that GNRH2 and GNRHR2 mediate LH-independent testosterone secretion from porcine testes. To further explore this ligand-receptor complex, a pig model with reduced GNRHR2 expression was developed. Small hairpin RNA sequences targeting porcine GNRHR2 were subcloned into a lentiviral-based vector, lentiviral particles were generated and microinjected into the perivitelline space of zygotes, and embryos were transferred into a recipient. One GNRHR2 knockdown (KD) female was born that subsequently produced 80 piglets from 6 litters with 46 hemizygous progeny (57% transgenic). Hemizygous GNRHR2 KD (n = 10) and littermate control (n = 7) males were monitored at 40, 100, 150, 190, 225 and 300 days of age; body weight and testis size were measured and serum was isolated and assayed for testosterone and luteinizing hormone (LH) concentrations. Body weight of GNRHR2 KD boars was not different from littermate controls (P = 0.14), but testes were smaller (P < 0.05; 331.8 vs. 374.8 cm3, respectively). Testosterone concentrations tended (P = 0.06) to be reduced in GNRHR2 KD (1.6 ng/ml) compared to littermate control (4.2 ng/ml) males, but LH levels were similar (P = 0.47). The abundance of GNRHR2 mRNA was reduced (P < 0.001) by 69% in testicular tissue from mature GNRHR2 KD (n = 5) versus littermate control (n = 4) animals. These swine represent the first genetically-engineered model to elucidate the function of GNRH2 and its receptor in mammals.

Interaction of dietary carbohydrate and fat on glucose metabolism in growing pigs.

Increased consumption of fructose has been suggested to be a contributing cause of the increased rates of obesity in humans. Rodent studies have shown an increase in de novo lipogenesis and decreased insulin sensitivity in response to feeding high levels of fructose, but it is unclear if these effects occur in the same progression in humans. We aimed to develop a swine model for studying changes in glucose metabolism and insulin resistance resulting from dietary carbohydrate alone or in combination with high dietary fat. Two experiments were conducted to determine if the source of dietary carbohydrate, with or without added fat, had an effect on body weight gain, glucose metabolism, or insulin response in growing pigs. In the first experiment, pigs (24 barrows, initial body weight 28 kg) were fed one of 4 diets in which the source of carbohydrate was varied: 1) 20% starch; 2) 10% glucose + 10% starch; 3) 10% fructose + 10% starch; and 4) 20% fructose for 9 weeks. There were no differences in growth rate or glucose clearance observed. Experiment 2 was conducted as a 3 × 2 factorial with the main effects of carbohydrate source (20% starch, glucose, or fructose) and added fat level (0 vs 10%). Pigs (24 barrows, initial body weight 71 kg) were fed one of 6 experimental diets for 9 weeks. Compared to the other dietary treatments, pigs fed fructose with high fat had an elevated glucose area under the curve during the GTT (Carbohydrate x Fat interaction, P < 0.01). This same group had a lower insulin response (Carbohydrate x Fat, P < 0.05). This work demonstrates that pigs can be a viable model to assess the long-term effects of dietary carbohydrates on metabolism and body composition. Studies of longer duration are needed to determine if these changes are indicative of insulin resistance.

Physiological and genomic insight into neuroendocrine regulation of puberty in gilts.

The timing of pubertal attainment in gilts is a critical factor for pork production and is an early indicator of future reproductive potential. Puberty, defined as age at first standing estrus in the presence of a boar, is brought about by an escape from estrogen inhibition of the GnRH pulse generator, which allows for increasing LH pulses leading to the onset of cyclicity. The biological mechanisms that control the timing of these events is related to decreasing inhibitory signals with a concomitant increase in stimulatory signals within the hypothalamus. The roles of gamma-aminobutyric acid, endogenous opioid peptides, and gonadotropin-inhibitory hormone in negatively regulating gonadotropin secretion in gilts is explored. Developmental changes in stimulatory mechanisms of glutamatergic and kisspeptin neurons are important for increased LH pulsatility required for the occurrence of puberty in pigs. Age at first estrus of gilts is metabolically gated, and numerous metabolites, metabolic hormones, and appetite-regulating neurotransmitters have been implicated in the nutritional regulation of gonadotropin secretion. Leptin is an important metabolic signal linking body energy reserves with age at puberty in gilts. Leptin acting through neuropeptide Y and proopiomelanocortin neurons in the hypothalamus has important impacts on the function of the reproductive neurosecretory axis of gilts. Age at puberty in swine is heritable, and genomic analyses reveal it to be a polygenic trait. Genome-wide association studies for pubertal age in gilts have revealed several genomic regions in common with those identified for age at menarche in humans. Candidate genes have been identified that have important functions in growth and adiposity. Numerous genes regulating hypothalamic neuronal function, gonadotropes in the adenohypophysis, and ovarian follicular development have been identified and illustrate the complex maturational changes occurring in the hypothalamic-pituitary-ovarian axis during puberty in gilts.

Review: kisspeptin and reproduction in the pig.

The activation of the hypothalamic-pituitary axis is critical for the initiation and maintenance of reproductive cycles in pigs and is influenced by a number of factors, such as nutrition, metabolism and gonadal steroids. Kisspeptin is a neuropeptide that is expressed in discrete regions of the porcine hypothalamus and is positioned to mediate the action of many of these factors. The expression of kisspeptin in the pig hypothalamus does not appear to be regulated by gonadal steroids in the same way as other species. It is unclear if kisspeptin is mediating nutritional or metabolic effects on gonadotropin secretion in pigs as it takes large deficits in feed intake or BW to affect hypothalamic expression of the KISS1 gene in the porcine hypothalamus. There appears to be little genetic diversity in kisspeptin or its receptor that is useful for improving reproduction in swine. Both peripheral and central injection of kisspeptin strongly stimulates the secretion of gonadotropin hormones, LH and FSH, in gilts. Similarly, synthetic analogues have been developed and showed potential promise as tools to manage reproductive cycles in gilts and sows. Review of the literature nonetheless reveals that research on kisspeptin and its function in controlling reproduction in pigs has lagged that of other livestock species.

Intrauterine position and adjacent fetal sex affects fetal and placental growth throughout gestation, but not embryonic viability, in pigs selected for component traits of litter size.

Intrauterine position and sex of adjacent fetuses in litter bearing species have been implicated in physiological and behavioral differences of offspring. The effects of uterine position and sex status of flanking fetuses with crowded uterine conditions on fetal and placental growth rate was tested. Gilts were unilaterally hysterectomized-ovariectomized at 160 d of age and mated at approximately 280 d of age, with fetal harvest at 45, 65, 85, or 105 d of gestation. Uterine position relative to the cervix, fetal status (alive, dead, sex), fetal weight, and placental weight were recorded at harvest. Each fetus was coded as adjacent to 0, 1, or 2 opposite sex fetuses and analyzed using an ANOVA fitting contemporary group, line, and flanking fetal sex code as fixed effects with sire as a random effect. The fraction of live fetuses in each classification (0, 1, 2) was 26.4%, 50.1%, and 23.4%, respectively, indicating no effect on fetal survival. Fetal weight was affected by flanking sex status between 65 d (P < 0.05) and 105 d (P < 0.001), with means at 105 d of 800.0 ± 20.3, 748.5 ± 17.8, and 672.7 ± 25.2 g, respectively for flanking sex status codes 0, 1, 2. Placental weight was similarly affected (P < 0.01) by flanking sex code, but only at 105 d. It is concluded that fetal growth and placental development in pigs is influenced by sex status of adjacent fetuses. This could be a potential source of variation in behavioral and reproductive differences later in life.

Energy metabolism and leptin: effects on neuroendocrine regulation of reproduction in the gilt and sow.

It is well established that reproductive function is metabolically gated. However, the mechanisms whereby energy stores and metabolic cues influence appetite, energy homeostasis and fertility are yet to be completely understood. Adipose tissue is no longer considered as only a depot to store excess energy. Recent findings have identified numerous genes, several neurotrophic factors, interleukins, insulin-like growth factor binding protein-5, ciliary neurotrophic factor and neuropeptide Y (NPY) as being expressed by adipose tissue during pubertal development. These studies demonstrated for the first time the expression of several major adipokines or cytokines in pig adipose tissue which may influence local and central metabolism and growth. Leptin appears to be the primary metabolic signal and is part of the adipose tissue-hypothalamic regulatory loop in the control of appetite, energy homeostasis and luteinizing hormone (LH) secretion. Leptin's actions on appetite regulation are mediated by inhibition of hypothalamic NPY and stimulation of proopiomelanocortin. Its effects on gonadotropin-releasing hormone (GnRH)/LH secretion are mediated by NPY and kisspeptin. Thus, leptin appears to be an important link between metabolic status, the neuroendocrine axis and subsequent fertility in the gilt and sow.

Effect of feeding three lysine to energy diets on growth, body composition and age at puberty in replacement gilts.

This study evaluated the effect of diets differing in standard ileal digestible (SID) lysine on lysine intake, growth rate, body composition and age at puberty on maternal line gilts. Crossbred Large White×Landrace gilts (n=641) were fed corn-soybean diets differing in SID lysine concentration (%, g SID lysine:Mcal ME); diets were not isocaloric. Gilts received three grower, finisher diet combinations: low (0.68% lysine grower, 0.52% lysine finisher), medium (0.79% lysine grower, 0.60% lysine finisher) or high (0.90% lysine grower, 0.68% lysine finisher). Grower diets were fed from 100 until 142days of age, and finisher diets were fed until they reached 220days of age. Body weight (BW), backfat thickness (BF), and loin depth (LD) were recorded every 28days. From 160-220days of age, gilts were exposed daily to vasectomized boars and observed for behavioral estrus. Gilts fed the low lysine diet had lower average daily gain and BW (P<0.05), but not fat depth:LD ratio. The percentage of gilts that displayed natural estrus by 220days of age was low but not different among dietary treatments (low 27.7%, medium 31.0% and high 37.7%, respectively; P=0.1201). Gilts fed the high and medium diets reached puberty 10 and 6days earlier, however, than gilts fed the low lysine diet (P<0.05). The rate of puberty attainment may have been less because all gilts contracted porcine epidemic diarrhea (PEDv) just as boar exposure was to begin for the first group of gilts. Results from the present study indicate that growth rate and age at puberty can be altered by ad libitum fed diets that differ in SID lysine concentration.

GENOMICS SYMPOSIUM: Using genomic approaches to uncover sources of variation in age at puberty and reproductive longevity in sows.

Genetic variants associated with traits such as age at puberty and litter size could provide insight into the underlying genetic sources of variation impacting sow reproductive longevity and productivity. Genomewide characterization and gene expression profiling were used using gilts from the University of Nebraska-Lincoln swine resource population ( = 1,644) to identify genetic variants associated with age at puberty and litter size traits. From all reproductive traits studied, the largest fraction of phenotypic variation explained by the Porcine SNP60 BeadArray was for age at puberty (27.3%). In an evaluation data set, the predictive ability of all SNP from high-ranked 1-Mb windows (1 to 50%), based on genetic variance explained in training, was greater (12.3 to 36.8%) compared with the most informative SNP from these windows (6.5 to 23.7%). In the integrated data set ( = 1,644), the top 1% of the 1-Mb windows explained 6.7% of the genetic variation of age at puberty. One of the high-ranked windows detected (SSC2, 12-12.9 Mb) showed pleiotropic features, affecting both age at puberty and litter size traits. The RNA sequencing of the hypothalami arcuate nucleus uncovered 17 differentially expressed genes (adjusted < 0.05) between gilts that became pubertal early (<155 d of age) and late (>180 d of age). Twelve of the differentially expressed genes are upregulated in the late pubertal gilts. One of these genes is involved in energy homeostasis (), a function in which the arcuate nucleus plays an important contribution, linking nutrition with reproductive development. Energy restriction during the gilt development period delayed age at puberty by 7 d but increased the probability of a sow to produce up to 3 parities ( < 0.05). Identification of pleotropic functional polymorphisms may improve accuracy of genomic prediction while facilitating a reduction in sow replacement rates and addressing welfare concerns.

Selection for uterine capacity improves lifetime productivity of sows.

Selection for 11 generations for uterine capacity (UC) increased litter size in gilts by 1.6 more fully formed pigs at birth compared to an unselected control line (CO) despite averaging one less ovulation. The objective of the present study was to quantify line by parity interactions and characterize litter performance traits of sows in each line at later parities. Gilts farrowed in contemporary groups of 19 litters and were maintained through four parities if successfully mated in that contemporary group. A total of 243 litters and 2639 piglets were analyzed. Fixed effects of farrowing group, line, parity (1-4), and two-way interactions involving line were fitted. Sire (n=57) of the sow within farrowing group and line was fitted as a random effect. No significant line by parity interactions were observed. Parity effects were detected (P<0.01) for individual piglet birth weight, pre-weaning gain, and weaning weight. Parity effects were also detected (P<0.05) for total number born, average and total litter birth weight, and average and total litter weaning weight. Selection line differences for litter traits were detected (P<0.05) for number stillborn piglets and approached significance (P=0.06) for number of piglets weaned. Retention of sows in the herd was greater (P<0.05) with an average of 2.33 parities for the UC line females compared to 1.87 parities for the CO line. This resulted in favorable cumulative lifetime productivity of the UC line for total number of piglets born, number of piglets born alive, litter birth weight, number of piglets weaned and litter weaning weight.

Plasma concentrations of acyl-ghrelin are associated with average daily gain and feeding behavior in grow-finish pigs.

The objectives of this study were to determine the effect of sex, sire line, and litter size on concentrations of acyl-ghrelin and total ghrelin in plasma of grow-finish pigs and to understand the relationship of plasma concentrations of ghrelin with feeding behavior, average daily gain (ADG), and back fat in grow-finish swine. Yorkshire-Landrace crossbred dams were inseminated with semen from Yorkshire, Landrace, or Duroc sires. Within 24 h of birth, pigs were cross-fostered into litter sizes of normal (N; >12 pigs/litter) or small (S; ≤ 9 pigs/litter). At 8 wk of age, pigs (n = 240) were blocked by sire breed, sex, and litter size and assigned to pens (n = 6) containing commercial feeders modified with a system to monitor feeding behavior. Total time eating, number of daily meals, and duration of meals were recorded for each individual pig. Body weight was recorded every 4 wk. Back fat and loin eye area were recorded at the conclusion of the 12-wk feeding study. A blood sample was collected at week 7 of the study to quantify concentrations of acyl- and total ghrelin in plasma. Pigs from small litters weighed more (P < 0.05) and tended (P = 0.07) to be fatter than pigs from normal litters. Postnatal litter size did not affect ADG, feeding behavior, or concentrations of ghrelin in plasma during the grow-finish phase. Barrows spent more time eating (P < 0.001) than gilts, but the number of meals and concentrations of ghrelin did not differ with sex of the pig. Pigs from Duroc and Yorkshire sires had lesser (P < 0.0001) concentrations of acyl-ghrelin than pigs from Landrace sires, but plasma concentrations of total ghrelin were not affected by sire breed. Concentrations of acyl-ghrelin were positively correlated with the number of meals and negatively correlated with meal length and ADG (P < 0.05). A larger number of short-duration meals may indicate that pigs with greater concentrations of acyl-ghrelin consumed less total feed, which likely explains why they were leaner and grew more slowly. Acyl-ghrelin is involved in regulating feeding behavior in pigs, and measuring acyl-ghrelin is important when trying to understand the role of this hormone in swine physiology.

Relationship of glucocorticoids and hematological measures with feed intake, growth, and efficiency of finishing beef cattle.

The objective of this experiment was to determine the association of glucocorticoids and markers for immune status in finishing beef steers and heifers with DMI, growth, and efficiency. Steers ( = 127) and heifers ( = 109) were individually fed a finishing ration for 84 d with BW measured every 21 d. Blood samples were collected via jugular venipuncture for metabolite (glucose and lactate) and cortisol analysis and rectal grab samples of feces were collected for corticosterone analysis on d 83 of the experiment. Plasma cortisol was not correlated to DMI ( = -0.08, > 0.05) or fractional DMI (g DMI/kg BW; = -0.03, > 0.05) but was negatively correlated with ADG ( = -0.17, < 0.01) and G:F ( = -0.20, < 0.01) and positively correlated to residual feed intake (RFI; = 0.14, < 0.05). Fecal corticosterone was positively correlated to fractional DMI ( = 0.15, < 0.05) and RFI ( = 0.23, < 0.01) and negatively correlated to G:F ( = -0.18, < 0.01). Using a mixed model analysis, none of the metabolites or hormones were associated with DMI ( > 0.05) but fecal corticosterone was positively associated with fractional DMI only in heifers ( = 0.04). Plasma lactate ( < 0.01) was and plasma cortisol ( < 0.10) tended to be negatively associated with ADG. Plasma cortisol ( < 0.05) and fecal corticosterone tended ( < 0.10) to be negatively associated with G:F. Fecal corticosterone was positively associated with RFI in heifers ( < 0.04). In a mixed model analysis, total leukocyte count was positively associated with ADG ( < 0.04) and tended to be positively associated with G:F ( < 0.06). Among leukocyte subtypes, neutrophil count was positively associated with ADG in steers ( < 0.02) and monocytes were positively associated with ADG in heifers ( < 0.03). Lymphocyte counts (LY) in steers were negatively associated with DMI ( = 0.03) and fractional DMI ( < 0.03). In heifers, LY tended to be positively associated with DMI ( < 0.09) and fractional DMI ( < 0.06). Lymphocyte count was also positively associated with ADG ( < 0.01) and G:F ( = 0.05) in heifers. The association of production traits with immune status seems to be different between steers and heifers. There was a stronger relationship of cortisol than fecal corticosterone to feed efficiency measures, suggesting that cortisol concentrations could be a better marker for feed efficiency traits than fecal corticosterone concentrations.

Litter-of-origin trait effects on gilt development.

The preweaning litter environment of gilts can affect subsequent development. In a recent experiment designed to test the effects of diet on gilt development, litter-of-origin traits including individual birth weights, immunocrits (a measure of colostrum intake), sow parity, number weaned, and individual weaning weights were collected for approximately 1,200 gilts that were progeny of approximately 300 sows. Subsequently, BW, LM area, and backfat were measured at 100 d of age and at 28-d intervals until slaughter (260 d of age). From 160 d of age to slaughter, gilts were observed daily for estrus. At slaughter, the reproductive tract and 1 mammary gland were recovered. The reproductive tract was classified as cyclic or prepubertal; the number of corpora lutea was counted. Uterine horn lengths and ovarian dimensions were measured. Uterus and ovary samples from every 10th gilt were prepared for histological evaluation of uterine gland development and follicle counts, respectively. Mammary gland tissue protein and fat were assayed. Day of the estrous cycle at slaughter was calculated using the first day of the most recent standing estrus (d 0) recorded previous to slaughter. Each gilt development trait was analyzed for association with each litter-of-origin trait, after adjusting for dietary treatment effects. Uterine length, ovarian dimensions, mammary gland protein and fat, and uterine gland development were also adjusted for day of the estrous cycle at slaughter. All litter-of-origin traits were associated ( < 0.05) with growth traits. Top-down (backward elimination) multiple regression analysis indicated that BW and LM accretion in gilts was positively associated with immunocrit ( < 0.01), birth weight ( < 0.01), preweaning growth rate ( < 0.01), and parity ( < 0.01). Backfat accretion was positively associated with preweaning growth rate ( < 0.01), number weaned ( < 0.05), and parity ( < 0.05). Age at puberty was associated with birth weight (positive; < 0.01) and preweaning growth rate (negative; < 0.01). Total uterine length was positively associated with only birth weights ( < 0.05). Mammary gland protein was negatively associated with preweaning growth ( < 0.01). Mammary gland fat was positively associated with birth weight and number of piglets weaned ( > 0.05). These results indicate that colostrum consumption, birth weights, preweaning growth rate, number weaned, and parity are associated with gilt development traits during later life.

Relationships between day one piglet serum immunoglobulin immunocrit and subsequent growth, puberty attainment, litter size, and lactation performance.

Colostrum affects gut and uterine gland development in the neonatal piglet, suggesting that subsequent growth and reproductive performance may be affected. Measuring immunoglobulin in piglet serum using the immunoglobulin immunocrit on Day 1 of age provides a simple, inexpensive indication of the amount of colostrum acquired by the piglet in the first day of life. Relationships between serum immunoglobulin immunocrit measures and subsequent growth rates, age at puberty, incidence of puberty failure, litter size, and lactation performance were examined in pigs born and subsequently farrowing between 2009 and 2013. Immunoglobulin immunocrit measures were collected on 16,762 piglets on Day 1 of age. Of these piglets, BW measurements were available from 15,324 (7,684 males and 7,640 females) piglets at a range of ages from weaning to 200 d of age, allowing an assessment of growth rates. Age at puberty was recorded from a subset of 2,857 of the females after observing them for estrous behavior from approximately 170 to 250 d of age. To examine relationships between d 1 immunocrit and puberty failure, gilts with immunocrit measures that failed to reach puberty (n = 119) were matched with littermate gilts with immunocrit measures that achieved puberty (n = 167). Similarly, number born alive was collected on a subset (n = 799) of females from first to fourth parities for which d 1 immunocrits were measured on them as neonates. Finally, d 1 immunocrit effect on adult lactational competence was assessed by measuring litter average (offspring of 440 females) and litter average piglet preweaning growth rate (offspring of 774 females) in females where d 1 immunocrits were available from them as neonates. Results indicated that low d 1 immunocrits were subsequently associated with reduced growth (P < 0.01), increased age at puberty (P < 0.01), reduced number born alive (P < 0.05), reduced litter average immunocrit (P < 0.05), and reduced litter average preweaning growth rate during lactation (P < 0.05). This suggests that management efforts to improve the amount of colostrum ingested by neonatal piglets would result in beneficial changes in production efficiency, particularly for gilts destined for the breeding herd. It also suggests that the immunoglobulin immunocrit can be useful in monitoring colostrum ingestion to maximize the beneficial effects of colostrum on subsequent performance.

Age at puberty, ovulation rate, and uterine length of developing gilts fed two lysine and three metabolizable energy concentrations from 100 to 260 d of age.

The objective of this study was to determine the effect of ad libitum feeding diets differing in standard ileal digestible (SID) lysine and ME concentrations that bracket those fed to developing gilts in U.S. commercial settings. Average SID lysine and ME concentrations in diets currently fed to developing gilts were obtained from a poll of the U.S. commercial swine industry. Crossbred Large White × Landrace gilts (n = 1,221), housed in groups, were randomly allotted to 6 corn-soybean diets in a 2 × 3 factorial arrangement formulated to provided 2 SID lysine and 3 ME concentrations. Gilts received grower diets formulated to provide 1.02% (control = survey average) or 0.86% (control minus 15%) SID lysine and 2.94, 3.25, or 3.57 (survey average ME ± 10%) Mcal of ME/kg from 100 d of age until approximately 90 kg BW. Then, gilts were fed finisher diet containing 0.85% (control = survey average) or 0.73% (control minus 15%) SID lysine and 2.94, 3.26, or 3.59 (control ± 10%) Mcal of ME/kg until 260 d of age. Gilts were weighed, and backfat thickness and loin muscle area were recorded at the beginning of the trial and then every 28 d. Starting at 160 d of age, gilts were exposed daily to vasectomized boars and observed for behavioral estrus. At approximately 260 d of age, gilts were slaughtered and their reproductive tract was collected. Each reproductive tract was examined to determine whether the gilt was cyclic, the stage of estrus cycle, ovulation rate, and uterine length. Data were evaluated for normality and analyzed using mixed model methods. Average age at puberty was 193 d of age with a range from 160 to 265 d. When all gilts on trial at 160 d of age were included in the analysis, 91.0% reached puberty as determine by observation of standing estrus. Differences between dietary treatments on age at puberty or measurements of the reproductive tract were not detected. Growth rates to 160 d were not limiting for attainment of puberty in response to daily boar stimulation from 160 d.

A polymorphism in myostatin influences puberty but not fertility in beef heifers, whereas µ-calpain affects first calf birth weight.

The use of genetic markers to aid in selection decisions to improve carcass and growth characteristics is of great interest to the beef industry. However, it is important to examine potential antagonistic interactions with fertility in cows before widespread application of marker-assisted selection. The objective of the current experiment was to examine the influence of 2 commercially available markers currently in use for improving carcass traits, the myostatin (MSTN) F94L and µ-calpain (CAPN1) 316 and 4751 polymorphisms, on heifer development and reproductive performance. In Exp. 1, beef heifers (n = 146) were evaluated for growth and reproductive traits over a 3-yr period to determine if these polymorphisms influenced reproductive performance. In Exp. 2, heifers representing the 2 homozygous genotypes for the MSTN F94L polymorphism were slaughtered on d 4 of the estrous cycle and reproductive tracts were collected for morphological examination. In Exp. 1, there was a tendency (P = 0.06) for birth BW to be affected by MSTN with the Leu allele increasing birth BW in an additive fashion. Additionally, MSTN significantly affected the proportion of pubertal heifers by the start of the breeding season (P < 0.05) with the Leu allele additively decreasing the proportion pubertal; however, this did not result in a delay in conception or a decrease in pregnancy rates during the first breeding season (P > 0.15). The GT haplotype of CAPN1, which was previously associated with decreased meat tenderness, was associated with an additive decrease in birth BW of the first calf born to these heifers (P < 0.05). In Exp. 2, there were no differences between the MSTN genotypes for gross or histological morphology of the anterior pituitary, uterus, or ovaries (P > 0.05). From these results, we concluded that the MSTN F94L and CAPN1 polymorphisms can be used to improve carcass traits without compromising fertility in beef heifers. The influence of these markers on cow performance and herd life remains to be determined. While the delay in puberty associated with the MSTN F94L polymorphism did not negatively impact reproductive performance in heifers, caution should be used when combining this marker with other markers for growth or carcass traits until the potential interactions are more clearly understood.

Body condition at parturition and postpartum weight changes do not influence the incidence of short-lived corpora lutea in postpartum beef cows.

Seventy-seven multiparous beef cows (Hereford and Angus x Hereford) with thin to moderate BCS at calving were used to evaluate the effects of body condition at parturition and BW change after calving on duration and occurence of luteal activity before and after first estrus. Blood samples were collected twice weekly after parturition to determine the occurrence of the first postpartum luteal activity (LA, progesterone > or = 0.5 ng/mL). Weight changes and BCS were determined at 2-wk intervals. Cows were exposed to bulls and observed twice daily for behavioral estrus. Luteal activity was classified as normal if plasma concentrations of progesterone were > or = 0.5 ng/mL for at least 11 d, or short if concentrations of progesterone were > or = 0.5 ng/mL for 10 d or less. The interval from parturition to first normal LA was shorter (P < 0.001) for moderate condition (BCS > or = 4.5) than for thin (BCS < or = 4) cows (58.3 +/- 3.2 vs. 93.3 +/- 5.1 d, respectively). Interval to first estrus also was shorter (P < 0.001) for moderate than for thin cows (53.3 +/- 3.7 vs. 89.3 +/- 5.6 d, respectively). Before the first normal LA, 78% of cows had an increase in progesterone for < 11 d. Postpartum weight change and BCS at calving did not influence the incidence of estrus associated with first normal LA. After the first estrus, 72% of cows had normal LA, 16% had a short luteal phase, and 12% lacked LA. Postpartum weight change and BCS did not influence the length of LA associated with the first estrus. Cows with normal LA had increased (P < 0.05) maximal concentrations of progesterone compared with cows that had a short luteal phase. When a transient increase in progesterone occurred before first behavioral estrus, 81% of cows had normal luteal function after estrus. We conclude that when beef cows are in thin to moderate body condition at calving, postpartum BW change and BCS at calving do not influence the duration of luteal activity before or after the first postpartum estrus.

Growth hormone response to growth hormone-releasing hormone in beef cows divergently selected for milk production.

In dairy cattle, increased circulating growth hormone has been associated with selection for greater milk yield. This study tested the hypothesis that beef cows divergently selected for milk production would have differing GH responses to a challenge dose of GHRH. Growth hormone response to a challenge of GHRH was measured in 36 Angus-sired cows ranging from 6 to 10 yr of age. The cows were classified as high milking (n = 16) or low milking (n = 20), on the basis of their sires' milk EPD. Mean milk EPD (in kilograms) were 16.6 and -14.4 for high and low milking cows, respectively. Milk production was estimated by the weigh-suckle-weigh procedure. Blood samples were taken immediately before and 10 min after a clearance dose of 4.5 microg of GHRH/100 kg BW (injected i.v.) and, 3 h later, immediately before and 10 min after a challenge dose of either 1.5 or 4.5 microg of GHRH/100 kg BW. Each animal received both challenge doses, and the doses were randomly assigned across 2 d of blood collection. Serum concentrations of GH and IGF-I were measured by RIA. Serum IGF-I was measured in the baseline blood sample on d 1 of blood collection. A positive relationship (r = 0.35; P = 0.03) was observed between the cows' rankings for each dose of GHRH; that is, high responders to the low dose were high responders to the high dose. Growth hormone response to the 4.5 microg/100 kg BW challenge dose of GHRH was positively related to sire milk EPD (R2 = 0.09; P = 0.03). Response of GH to the 1.5 microg GHRH/100 kg BW challenge dose also tended to be related (P = 0.08) to sire milk EPD of high milking cows. In addition, IGF-I concentrations of high milking cows were inversely related (R2 = 0.24; P = 0.04) to sire milk EPD. Growth hormone response to GHRH challenge may have potential as an additional tool in the evaluation of milk production in beef cattle.

Effects of supplementation on intake, digestion, and performance of beef cattle consuming fertilized, stockpiled bermudagrass forage.

Experiments were conducted to determine the effects of increasing supplement protein concentration on performance and forage intake of beef cows and forage utilization of steers consuming stockpiled bermudagrass forage. Bermudagrass pastures were fertilized with 56 kg of N/ha in late August. Grazing was initiated during early November and continued through the end of January each year. Treatments for the cow performance trials were: no supplement or daily equivalents of 0.2, 0.4, and 0.6 g of supplemental protein per kilogram of BW. Supplements were formulated to be isocaloric, fed at the equivalent of 0.91 kg/d, and prorated for 4 d/wk feeding. Varying the concentration of soybean hulls and soybean meal in the supplements created incremental increases in protein. During yr 1, supplemented cows lost less weight and condition compared to unsupplemented animals (P < 0.05). During yr 2, supplemented cows gained more weight (P = 0.06) and lost less condition (P < 0.05) compared to unsupplemented cows. Increasing supplement protein concentration had no affect on cumulative cow weight change or cumulative body condition score change. Forage intake tended to increase (P = 0.13, yr 1 and P = 0.07, yr 2) in supplemented cows. Supplement protein concentration did not alter forage intake. In a digestion trial, four crossbred steers were used in a Latin square design to determine the effects of supplement protein concentration on intake and digestibility of hay harvested from stockpiled bermudagrass pasture. Treatments were no supplement; or 0.23, 0.46, and 0.69 g of supplemental protein per kilogram of BW. Forage intake increased (P < 0.05) 16% and OM intake increased (P < 0.01) 30% in supplemented compared to unsupplemented steers. Diet OM digestibility increased (P = 0.08) 14.5% and total digestible OM intake increased (P < 0.05) 49% in supplemented compared to unsupplemented steers. Supplement protein concentration did not alter forage intake, total digestible OM intake, or apparent digestibility of OM or NDF. During the initial 30 d after first killing frost, beef cows did not respond to supplementation. However, later in the winter, supplementation improved utilization of stockpiled bermudagrass forage.

Influence of body condition at calving and postpartum nutrition on endocrine function and reproductive performance of primiparous beef cows.

The influences of body condition score (BCS) at calving and postpartum nutrition on endocrine and ovarian functions, and reproductive performance, were determined by randomly allocating thin (mean BCS = 4.4 +/- 0.1) or moderate condition (mean BCS = 5.1 +/- 0.1) Angus x Hereford primiparous cows to receive one of two nutritional treatments after calving. Cows were fed to gain either 0.45 kg/d (M, n = 17) or 0.90 kg/d (H, n = 17) for the first 71 +/- 3 d postpartum. All cows were then fed the M diet until 21 d after the first estrus. A replication (yr 2; M, n = 25; H, n = 23) was also used to evaluate reproductive characteristics. Concentrations of IGF-I, leptin, insulin, glucose, NEFA, and thyroxine were quantified in plasma samples collected weekly during treatment and during 7 wk before the first estrus. Estrous behavior was detected by radiotelemetry, and luteal activity was determined based on concentrations of progesterone in plasma. All cows were bred by AI between 14 and 20 h after onset of estrus, and pregnancy was assessed at 35 to 55 d after AI by ultrasonography. Cows that calved with a BCS of 4 or 5 had similar endocrine function and reproductive performance at the first estrus. During treatment, H cows gained BW and increased BCS (P < 0.01), and had greater (P < 0.05) concentrations of IGF-I, leptin, insulin, glucose, and thyroxine in plasma than M cows. However, during the 7 wk before the first estrus, plasma concentrations of IGF-I, leptin, insulin, glucose, NEFA, and thyroxine were not affected by time. Cows previously on the H treatment had a shorter (P < 0.01) interval to first postpartum estrus and ovulation, and a larger dominant follicle (P < 0.01) at first estrus, than M cows, but duration of estrus and the number of mounts received were not influenced by nutrient intake. Pregnancy rate at the first estrus was greater (P < 0.03) for H (76%, n = 38) than for M (58%, n = 33) cows. Increased nutrient intake after calving stimulated secretion of anabolic hormones, promoted fat deposition, shortened the postpartum interval to estrus, and increased pregnancy rate at the first estrus. Concentrations of IGF-I and leptin in plasma were constant during 7 wk before the first estrus, indicating that acute changes in these hormones are not associated with the resumption of ovarian function in primiparous beef cows.

Efficacy of intramuscular treatment of beef cows with oxytetracycline to reduce mastitis and to increase calf growth.

Spring-calving multiparous Angus x Hereford cows were used to determine the efficacy of intramuscular treatment with oxytetracycline to reduce the incidence of mastitis-causing bacteria, decrease milk somatic cell counts (SCC), and increase calf growth. During 2 yr, milk samples were collected from each quarter from a total of 319 cows at 8 to 14 d after calving and at weaning, to determine the presence of bacteria and SCC. A California mastitis test (CMT) was performed on milk from each quarter of each cow at the initial sample collection. Cows with a CMT score of 1, 2, or 3 in at least one quarter, were randomly assigned to receive either an intramuscular injection of oxytetracycline (n = 63) or the control vehicle (n = 60), and cows with a CMT score of 0 or trace in all four quarters were not treated (n = 196). Calf weights were determined at birth, early lactation, and weaning. The number of somatic cells in milk and the percentage of quarters that were infected increased as CMT score increased (P < 0.01). The presence of mastitis-causing bacteria at calving increased (P < 0.05) the incidence of infection at weaning. The presence of mastitis-causing bacteria at weaning was associated with increased SCC for quarters and average SCC for cows (P < 0.01). Average SCC per cow at weaning increased (P < 0.05) as the number of infected quarters per cow increased. Treatment did not alter (P > 0.10) the percentage of cows or quarters infected with mastitis-causing bacteria or SCC of cows or quarters at weaning. Average SCC per cow was negatively correlated (P < 0.05) with calf weights at early lactation, but not with weaning weights of calves. Treatment did not influence (P > 0.10) calf weights at early lactation or at weaning. Cows with one or more dry quarters after calving had calves that weighed less at early lactation and weaning than cows with four functional quarters (P < 0.01). Intramuscular oxytetracycline treatment of beef cows that had CMT scores of 1 or greater after calving did not reduce intramammary infection rates or increase calf weights at weaning.