Clinical utility of plasma progesterone and blood and plasma glucose concentrations in predicting parturition in Holstein cows.

An accurate, practical, and low-cost method for predicting parturition is urgently needed in the dairy industry. The objective of this study was to evaluate changes in plasma progesterone concentration ([prog]) and glucose concentration in whole blood ([gluc]b) and plasma ([gluc]p) as predictors of parturition within 6, 12, and 24 h in primiparous and multiparous Holstein cows. Blood samples were obtained daily at approximately 0900 h from 34 primiparous and 72 multiparous Holstein cows in late gestation and the time of calving recorded to the nearest hour. Plasma [prog] was measured using an ELISA, and [gluc]b and [gluc]p using a low-cost point-of-care glucose meter. The optimal cut-point for predicting parturition was determined using binomial logistic regression with general estimating equations, because the data set consisted of repeated measures for each cow. Diagnostic test performance was evaluated by comparing the area under the receiver operating characteristic curve (AUC) and calculating the sensitivity, specificity, and κ at the optimal cut-point for predicting parturition. Plasma [prog] was the most accurate predictor of parturition within 24 h (AUC = 0.96) and 12 h (AUC = 0.93), whereas [gluc]b was the most accurate predictor of parturition within 6 h (primiparous, AUC = 0.96; multiparous, AUC = 0.86). We conclude that a decrease in plasma [prog] is currently the most accurate test for predicting calving within 24 h. Measurement of [gluc]b is a promising new test for the cow-side prediction of parturition in dairy cows due to its accuracy, practicality, and low cost.

Evaluation of forage soybean, with and without pearl millet, as an alternative for beef replacement heifers.

Apparent ruminal digestibility of forage soybean-based silages, with and without pearl millet, was determined along with evaluation of silages on heifer performance and reproductive function. Fermenters were utilized in a Latin square design and randomly assigned to 1 of the following treatments: 1) control diet of alfalfa haylage (CON), 2) soybean silage (SB) or 3) soybean and pearl millet silage (SB×PM). All diets were formulated to meet or exceed nutrient requirements of replacement beef heifers targeted to gain 0.79 kg/d. These same diets were fed to 90 Angus-Simmental beef replacement heifers [body weight (BW) = 366 kg; body condition score (BCS) = 5.53; age = 377 ± 11 d] 65 d prior to timed artificial insemination (TAI). Heifers were randomly allotted by breed, BCS and BW to 1 of the 3 treatments, with 3 reps/treatment. Diets were terminated 21 d post-TAI and heifers were commingled and placed on a common diet. Pubertal status was determined by progesterone concentrations of 2 blood samples taken 10 d apart prior to both trial initiation as well as initiation of estrous synchronization. Ovulatory follicle diameter was determined at time of breeding by ultrasonography. Pregnancy diagnosis was accomplished 35 and 66 d post-TAI, respectively, to calculate TAI and end of season pregnancy rates. Neither SB nor SB×PM had an effect (P > 0.37) on apparent ruminal digestion of nutrients compared to the CON. Final BW (414 kg; P ≥ 0.10) and BCS (5.28; P ≥ 0.26) for the heifers were similar among treatments. Likewise, there were no differences in TAI (48%; P > 0.43) or overall breeding season (93%; P > 0.99) pregnancy rates. Ovulatory follicle diameters (11.7 mm) was not different (P > 0.19) among treatments. In summary, forage soybean-based silages, with and without pearl millet, was an acceptable alternative forage for developing replacement beef heifers.

Ovariectomy as a means of abortion and control of estrus in feedlot heifers.

Three hundred and six heifers were randomly assigned to treatment groups in a three by six factorial design. Treatments were ovariectomy, melengestrol acetate (MGA), manual abortion, intramuscular estradiol cypionate (ECP) or Prostaglandin F2alpha and untreated controls. The Average Daily Gain (ADG) of the Ovariectomized Group was less (p < .01) during the first 24 days and not different (p > .05) for the total feeding period. Feed intake of the Ovariectomized Group was less (p < .05) than Manual Abortion, Prostaglandin or Control Groups during the first 24 days but essentially the same (p > .05) for the total period. The Prostaglandin Group required fewer days to reach slaughter condition than the Ovariectomy or MGA Groups (p < .05). The only difference in the cost/benefit analysis was in the direct cost of the treatments. Factors other than the various treatments interrupted many pregnancies. The effects of treatments varied with 100% of pregnancies terminated only in the Prostaglandin F2alpha Group.

Estimation of net energy requirements (NEm and NE delta) of lactating beef cows.

Spring-calving Angus cows (n = 24) in moderate body condition were assigned to either a high (H), maintenance-high (MH) to support superior milk, maintenance-low (ML) to support average milk, or low (L) energy diet at 12 d (SD = 4) postpartum. Energy balance for individual cows was determined by body condition change, weight change, and weigh-suckle-weigh milk production estimates. High energy intake increased (P < .05) BW, body condition score (BCS), and megacalories of body energy (BE) by 94 d postpartum. Neither dietary nor BCS accounted for significant (P > .30) variation in days to first ovulation or conception. Fasting heat production was estimated to be 72.5 kcal/BW.75 from the regression of log daily heat production/BW.75 on daily ME intake/BW.75. Rate of daily BW change did not affect concentration of energy in the weight change. Body condition score change was highly correlated (r = .98) to BW change, with each unit of BCS (1 to 5 scale) change associated with 68 kg of BW change. Two methods were used to determine NE for weight change (NE delta) based on empty body weight (EBW) change. Method 1 used the equation: BCS change = -.404 + .0147 (BW change) and Method 2 used only the regression coefficient of this equation to predict daily BCS change. Methods 1 and 2 resulted in similar regression equations: NE delta (Mcal/kg EBW change) = 1.590 + 1.251 (BCS) and NE delta (Mcal/kg EBW change) = 1.317 + 1.251 (BCS). Ranges of estimated protein and lipid in the EBW change, respectively, were 10.0 to 13.7% and 17.1 to 77.2%.

Adipose tissue lipogenesis in growing steers adapted to different levels of feed intake.

The association between feed intake and lipogenic activity in adipose tissue was investigated in growing cattle. Twenty-five 300-kg steers were allotted by BW to one of five levels of intake of a single high-energy corn-corn silage-based diet. Steers were adapted to diets over 4 wk and intakes were adjusted weekly to achieve steady but varying rates of growth. Daily intakes (% of BW) averaged .92, 1.15, 1.64, 2.28 and 2.69 and resulted in growth rates over the final 3 wk of -.28, .07, .71, 1.67 and 1.69 kg/d, respectively. Lipogenic activities in biopsied tissue and circulating concentrations of glucose and insulin were lowest at maintenance feeding and below but increased linearly (P less than .01 for lipogenesis; P less than .1 for glucose and insulin) as intake increased above maintenance. Mean minimal and maximal rates (mumoles.-min(-1).10(6) cells(-1)) or concentrations were fatty acids synthesis ([14C]acetate---fatty acid)), .065 and .723; fatty acid synthetase (NADPH oxidized), .266 and 2.97; lipoprotein lipase (fatty acid released), .048 and .359; glucose (mg/dl), 60.4 and 70.7 and insulin (ng/ml), .70 and 1.66. In a preliminary study with the same 25 steers fed ad libitum, nearly 25% of the variability in adipose tissue lipogenesis was accounted for by variation in feed intake. Results indicate that activities of lipogenic enzymes and lipogenic capacity in growing steers coordinately adapt to the level of feed consumed and that nutrient availability and(or) insulin concentrations may participate in this adaptation.

Effect of suppression of prolactin secretion on adipose lipogenesis in the postpartum beef cow.

Effects of inhibiting prolactin secretion and of calf removal at 3 d postpartum on the lipogenic capacity of s.c. adipose tissue were investigated in postpartum beef cows. The rate of fatty acid synthesis (SYN) from [1-14C]acetate and the activity of fatty acid synthetase (FAS) were assessed on adipose tissue obtained by biopsy at 1, 2, 4, 8 and 10 wk postpartum. Administration of bromocriptine (BR; a drug that suppresses prolactin secretion in rats) between d 7 and 42 postpartum decreased average serum prolactin concentrations nearly 90%, but BR had no effect on lipogenic rates at any week compared to control (CO) cows. Rates of SYN (nmol acetate.min-1.g-1 tissue) increased linearly in CO and BR cows from a nadir of 3.1 at wk 1 to 19.3 by wk 8. Within CO and BR, cows with the greater energy intake relative to requirements for lactation (energy balance) had the faster rates of recovery of SYN. Cows whose calves were weaned early (3 d) showed rapid early increases in SYN, reaching an average maximum rate of 46.2 by wk 2. Activity of FAS generally followed a pattern similar to that of SYN for all groups. Results indicate that prolactin is not responsible for low rates of postpartum lipogenesis in s.c. adipose tissue and that energy intake influences the rate of recovery.

Induction of estrus in ovariectomized cows and heifers: effects of estradiol benzoate and gonadotropin releasing hormone.

Three experiments were conducted with ovariectomized (OVX) cows and heifers to investigate potential neuroendocrine mechanisms controlling estrous behavior. In Exp. 1, 10 OVX cows were treated with either 125 micrograms estradiol benzoate and 10 cc saline (125 micrograms EB + SAL), 125 micrograms EB and 500 micrograms gonadotropin releasing hormone (125 micrograms EB + GnRH), 250 micrograms EB and 10 cc SAL (250 micrograms EB + SAL), 250 micrograms EB and 500 micrograms GnRH (250 micrograms EB + GnRH) or 500 micrograms EB and 10 cc SAL (500 micrograms EB + SAL) in a replicated 5 X 5 Latin-square design. During the 48 h following EB injection, 2-h observation blocks were alternated with 2-h non-observation blocks. During each 2-h observation block, 14 behavioral interactions were monitored. The percentage of cows in estrus was lower for cows receiving 125 micrograms EB as compared with those given the higher doses. However, the cows receiving 125 micrograms EB + SAL did not differ in their estrous response from those receiving 125 micrograms EB + GnRH. The interval from injection to the onset of estrus and the duration of estrus were similar for all treatments. In Exp. 2, 10 OVX heifers were subjected to the same treatments and observation procedures utilized in Exp. 1. The results of Exp. 2 were similar to those of Exp. 1. In Exp. 3, 10 OVX cows were treated with either 300, 600, 1,200, 2,400 or 4,800 micrograms EB in a replicated 5 X 5 Latin-square design.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of body composition, pre- and postpartum energy level and early weaning on reproductive performance of beef cows and preweaning calf gain.

Mature Charolais x Angus rotational cross cows were adjusted to moderate body condition by d 190 of gestation then randomly blocked to a maintenance (ME) or low-energy (LE) diet. At parturition, the 128 cows were randomly allotted within prepartum (PRP) diet to a high-energy (HE) or LE diet. At d 30 postpartum (PP), cows were randomly blocked to two treatments in which calves were weaned early (EW) or normally (NW) at 7 mo of age. Cows receiving a LE PRP diet had lighter calves at birth (34.7 vs 39.0 kg) and 105 d (127.9 vs 144.6 kg). Prepartum and PP energy interacted to affect postpartum anestrous interval (PPI, d) and cycling activity (%), respectively (LE-LE = 72.6, 33.3; LE-HE = 54.3, 56.3; ME-LE = 65.7, 52.9; ME-HE = 68.4, 54.3). High PP energy averaged over PRP diet increased (P less than .10) pregnancy rate by 22.7% and 105-d calf weight by 15.1 kg. Early weaning reduced PPI by 24.3 d (P less than .01) and first service conception rate by 21.7% (P less than .10). Cycling activity within 60 d PP was affected (P less than .01) by PRP diet and suckling status (LE-EW = 62.5, LE-NW = 26.7, ME-EW = 88.9, ME-NW = 13.3%). Thin cows had a longer PPI but had a higher first service conception rate than moderate and fleshy cows. Higher pregnancy rates were observed in cows approaching or maintaining average body condition from parturition to conception than for cows moving away from moderate body condition. Results suggest that fleshy and thin cows at parturition should be managed to approach moderate body condition before the breeding season to optimize reproductive performance and preweaning calf gain.

Influence of cortisol and dexamethasone on estrous behavior of estradiol-treated ovariectomized cows and heifers.

Two experiments were conducted with estradiol-treated ovariectomized cows and heifers to determine if cortisol and dexamethasone inhibit estrous behavior. In Experiment 1, eight ovariectomized Holstein cows were subjected to weekly hormonal treatments in a replicated 4 X 4 Latin square. Treatments consisted of 500 micrograms estradiol benzoate and either 0, 40, 80, or 160 mg cortisol. During the 48 h after hormonal injection, 2-h periods of observation were alternated with 2-h periods of no observation. During each observation period, cows were observed continuously for 14 behavioral interactions that increase in frequency at estrus. Percentage of cows exhibiting estrus, interval from injection of hormones to the onset of estrus, duration of estrus, and total numbers of each behavioral interaction were similar for all treatments. In Experiment 2, 10 ovariectomized Holstein heifers were subjected to weekly hormonal treatments in a replicated 5 X 5 Latin square. Treatments consisted of 500 micrograms estradiol benzoate and either 4 mg dexamethasone, 0, 50, 100, or 200 mg cortisol. The estradiol benzoate plus dexamethasone treatment tended to lower the percentage of cattle exhibiting estrus. Interval from injection to onset of estrus, duration of estrus, and total numbers of each behavioral interaction were similar for all treatments. These data indicate that cortisol given with estradiol did not inhibit estrus in ovariectomized cows and heifers, whereas dexamethasone tended to inhibit induced estrus.

Influence of dexamethasone, progesterone, gonadotropin-releasing hormone, and testosterone on estrous behavior of estradiol-treated ovariectomized heifers.

In Experiment 1, 12 ovariectomized heifers were assigned to receive weekly hormone treatments in a replicated 6 x 6 Latin square design. Hormonal treatments were given as two simultaneous injections i.m. and consisted of: 1) 2 ml propylene glycol and 2 ml propylene glycol; 2) .5 mg estradiol benzoate and 2 ml propylene glycol; 3) .5 mg estradiol benzoate and 4 mg dexamethasone; 4) .5 mg estradiol benzoate and 10 mg progesterone; 5) .5 mg estradiol benzoate and .4 mg GnRH; and 6) .5 mg estradiol benzoate and 12.5 mg testosterone propionate. The .5 mg estradiol benzoate and 4 mg dexamethasone treatment reduced the percentage of heifers in estrus compared with the .5 mg estradiol benzoate and 2 ml propylene glycol treatment. In Experiment 2, 16 ovariectomized heifers were used in four replicates of a 4 x 4 Latin square design to determine if pretreatment with progesterone potentiated the actions of estradiol. Hormonal treatments i.m. consisted of: 1) 0 mg progesterone and .2 mg estradiol benzoate; 2) 50 mg progesterone and .2 mg estradiol benzoate; 3) 0 mg progesterone and .5 mg estradiol benzoate; and 4) 50 mg progesterone and .5 mg estradiol benzoate. Progesterone pretreatment, at either dosage of estradiol benzoate, did not increase the percentage of heifers in estrus. Based on these observations, we conclude that: 1) dexamethasone inhibited estrus in estradiol-treated ovariectomized heifers and 2) progesterone pretreatment did not potentiate the actions of estradiol in ovariectomized heifers.