Age at puberty can influence the lifetime productivity of beef females. This study was conducted to determine the influence of hay quality, breed, and ovarian development on the onset of puberty and reproductive performance of beef heifers. Fifty-one 3/4 Hereford × 1/4 Angus (HA, Bos taurus ×X Bos taurus) and 45 3/4 Hereford × 1/4 Brahman (HB, Bos taurus × Bos indicus) heifers received ad libitum either high quality (HQ; NDF = 44.3%; CP = 19.5%) or low quality (LQ; NDF = 53.5%; CP = 18.3%) alfalfa (Medicago sativa L.) hay and 3.0 lb ground sorghum (Sorghum bicolor L. Moench.) grain/head/d. Puberty was defined by three criteria: (i) behavioral estrus, (ii) presence of a palpable corpus luteum, and (iii) serum progesterone above 1 ng/ml. Ultrasonography was used to determine bilateral ovarian follicular populations when heifers were 11 mo old. Heifers were inseminated artificially (AI) during a 49-d breeding period, and conception and pregnancy rates were determined by fetal aging via palpation per rectum. More HB than HA heifers were pubertal by 14 (P < 0.01) and 15 (P < 0.05) mo of age, whereas HA heifers reached puberty at lighter (P < 0.05) weights than HB heifers. A higher percentage of the heifers receiving HQ hay was pubertal by 16 mo of age (P = 0.08), and more HB heifers and heifers receiving HQ hay became pregnant during the AI breeding period (P = 0.10). Heifers bred at the pubertal estrus had lower (P < 0.05) conception rates at first service than heifers bred at a later estrus (52 vs. 88%). Diameter of the largest follicle was related to onset of puberty, and HB heifers with more follicles at 11 mo of age reached puberty at heavier weighs and older ages (P < 0.01). We conclude that onset of puberty and reproductive performance of beef heifers are influenced by hay quality and breed. In addition, onset of puberty appeared to be related to diameter of the largest follicle at 11 mo of age in both breed types and number of follicles at 11 mo of age in HB heifers.
Limit creep-feeding a 36% protein supplement (avg. salt concentration = 7.9%) was compared with unlimited consumption of the same supplement without salt (full creep-feeding) and with no supplementation. Average daily gain of steer calves was increased (P≤.06) by.19 (limit creep-feeding) and .38 (full creep-feeding) lb per day compared with non-supplemented calves. Average daily gain of heifer calves was not increased by creep feeding. Efficiency with which creep was converted to extra gain was poor for both limit and full creep-feeding groups. Little difference was observed in postweaning average daily gains; however, the calves given ad libitum access to creep feed tended (P=.12) to have greater daily gains (1.9 lbs) than non creep-feeding calves (1.6 lbs). Limit creep-fed calves had average daily gains of 1.7 lbs. Feed conversion during the post-weaning period was slightly improved (P=.09) in calves that had been given ad libitum access to creep feed.
The objective of this study was to determine the effect of natural mating stimuli on serum concentrations of LH, testosterone (T) and estradiol-17β (E2) in beef bulls. Twenty sexually experienced, yearling beef bulls were bled every 15 min during a 9-h period, 4 h before and 5 h after exposure to estrual females. For exposure, each bull was placed individually in an isolated pen with two restrained estrual heifers for 10 min or until one service was achieved. Timing and number of all behavioral events, including flehmen responses, abortive mounts and services, were recorded for each bull by two independent observers. Of the 20 bulls, 9 bulls mounted and were removed immediately after achieving a service, 8 bulls mounted widiout achieving a service and 3 bulls exhibited no interest during exposure. Twelve bulls achieved fewer than three and eight bulls achieved three or more flehmen responses during exposure. Postexposure responses in LH, T and E2 were not consistently correlated with number of mounts or presence or absence of a service. However, postexposure LH and T, but not E2, responses were highly correlated with number of flehmen responses achieved (r = .40 to .66; P = .08 to .001). In bulls that achieved three or more flehmen responses, serum LH increased within 30 min after exposure (P = .02) and serum T was increased dramatically within 1 h after exposure (P < .01), compared with preexposure hormone concentrations, regardless of the number of mounts and regardless of the presence or absence of a service. Natural mating stimuli had no effect on serum E2, and mounting activity alone and mounting that culminated in a service did not necessarily result in increased LH or T in beef bulls. However, number of flehmen responses achieved during exposure to females dramatically influenced postexposure serum LH and T concentrations in beef bulls.
Two experiments were conducted to evaluate the influence of supplemental protein concentration on the intake and utilization of dormant range forage by beef cattle. In Exp. 1,97 pregnant Hereford x Angus cows (avg wt = 454 kg) were assigned randomly to three isocaloric treatment supplements: 1) low protein (LP), 13% CP; 2) moderate protein (MP), 25% CP; and 3) high protein (HP), 39% CP. In Exp. 2, 15 ruminally and 12 esophageally cannulated steers (avg wt = 319 and 355 kg, respectively) were assigned randomly to LP, MP and HP treatments and were used in a 22-d winter grazing trial to evaluate forage intake and utilization characteristics. In Exp. 1, cow body condition (BC) and BW changes responded in linear (P less than .01) and quadratic (P less than .01) fashions to increasing protein concentration, with MP and HP displaying the least BC and BW loss from trial initiation (d 1) through d 84. From d 84 to calving (avg calving date = d 120), only the HP supplement continued to be effective in minimizing BC loss (P less than .01). Calf birth weight tended (P = .17) to increase in a linear fashion to increasing supplemental protein concentration, but calf ADG and cow reproductive efficiency were unaffected (P greater than .10). In Exp. 2, forage OM intake responded in a quadratic fashion (P less than .10), with the MP treatment having the highest NDF digestibility and ruminal OM fill. In conclusion, beef cow BC and BW losses during the winter grazing period were minimized with increasing supplemental CP concentration. Intake and utilization of dormant forage by steers were improved with moderate (26%) levels of CP in the supplement.
Four trials were conducted to evaluate the effectiveness of Melegestrol Acetate (MGA ®) and prostaglandin (PGF) in inducing and synchronizing estrus. In trial 1, treated heifers were fed MGA for 7 days and given a PGF injection on either the first or last day of MGA feeding. The 7-day estrus response was higher (P<.01) for treated heifers than untreated controls. In trial 2, treated cows were fed MGA for 7 days and given a PGF Injection on the last day of MGA feeding or 13 days after the last day of MGA feeding. The 7-day estrus response was also higher (P<.01) in treated cows. In trial 3, 59 cows were fed MGA for 7 days followed by a PGF injection, and exposed to bulls for 66 days. The MGA-PGF treatment was ineffective in synchronizing estrus and hastening conception. In trial 4, feeding MGA for 7 days successfully synchronized estrus in. cycling cows, but first service conception rates were reduced by 10% in the Kansas study and by 16% in a four state study.
Morbidity reduces performance and quality grade, but the effects of morbidity on quality grade independent of its effect on carcass fatness are rarely documented. As feedlot cattle fatten, a greater proportion of their daily carcass gain goes to fat deposition, and greater carcass fat is consistent with greater marbling score. Higher-grading cattle are often assumed to have reduced feedlot performance. Objectives of this research were to document the impacts of various animal and non-animal factors on feedlot average daily gain, health, and carcass traits in Angus steers and to correlate quality and yield grade components of carcass with live performance.
Feeding the ionophore monensin to yearling beef bulls improved (P<.05) weight gain by 4.2%. Final hip height was similar between treatments, but bulls fed monensin had almost 1 cm greater (P<.01) scrotal circumference and more than 10 cm 2 larger (P<.01) pelvic area. Semen characteristics generally were unaffected by treatment. However, bulls fed monensin had less (P<.01) semen motility than controls. Approximately 30 sperm morphology traits were evaluated; values were similar between treatments except for those traits listed. Collection date tended to influence (P<.15) volume, concentration, motility, and postfreeze characteristics.
Twelve first-calf, 2-year-old, Hereford heifers were randomly assigned in equal numbers on two levels of energy (17.6 Mcal DE/day and 11.4 Mcal DE/day) beginning 100 days prepartum. Jugular blood was collected three times weekly from the heifers starting 14 days before parturition, and continuing through the postpartum period until 20 days following the first estrus. There was no significant effect of nutrition on peripheral levels of progesterone or estradiol either prior to or following parturition. Progesterone levels declined from 2.0 to 2.5 ng/ml during late gestation to 0.7 to 0.9 ng/ml at parturition and remained low until just preceding the first postpartum estrus. Progesterone levels were higher immediately preceding the first postpartum estrus in those heifers that conceived. A short estrous cycle (6 to 8 days) was observed in three heifers following first estrus. In these, progesterone levels failed to exceed 0.6 ng/ml. Estradiol levels also declined sharply at parturition and remained in the range of 4 to 8 pg/ml during the postpartum period rising at the occurrence of first postpartum estrus.
Summary Eight years of records for 1495 beef heifers from two Kansas herds were analyzed to determine some of the causes of dystocia in primiparous heifers and its effects on subsequent reproductive performance and weaning weights of progeny. Records from spring calving Simmental (SS); fall calving Simmental (SF) and fall calving Angus (AF) heifers were analyzed. Percentages of heifers requiring assistance at first parturition for the SS, SF and AF were 57%, 38% and 36%, respectively. Calves requiring assistance produced heavier (P = .01) birth weight calves with increased (P=.01) ca lf mortality at birth. Conception rates during a subsequent 63 day breeding season followed first parturition were lower for assisted than unassisted dams. Assisted AF heifers were 7.96 days younger (P than unassisted AF heifers at their first parturition. Assisted SS heifers had a 12.58% lower (P .05) first service conception rate and 15.29% fewer (P assisted heifers calved in the first 21 days of the subsequent calving season than unassisted SS heifers. Calves from assisted SF heifers were 8.2 kg heavier (P .05) at weaning than calves from unassisted dams. Simmental heifers requiring assistance at their own birth tended to require more (P assistance at first parturition. Sire of dam had a significant effect on dam's reproductive and growth performance and on dam's progeny's weaning weight. Dystocia in first calf heifers was associated with heavier birth weights, increased calf mortility and reduced rebreeding, but did not reduce weaning weights of first or second calf.
Expanded use of artificial insemination in the beef cattle industry depends on successful application of treatments designed to synchronize estrus. Regulation of estrous cycles is associated with control of the corpus luteum (CL), whose life span and secretory activity are subject to trophic and lytic mechanisms. The advantages of melengestrol acetate (MGA) in estrous synchronization incorporate ease of administration, lower cost relative to other estrous synchronization products, and potential for use to induce estrus in prepubertal heifers. Treatments first designed to synchronize estrous cycles of normally cycling heifers by feeding MGA were imposed daily for 14 to 18 d at levels of .5 to 1 mg. The minimal daily effective dose required to inhibit ovulation was .42 mg. Longer feeding periods of MGA were associated with low fertility at the first synchronized estrus, but at the second estrus, conception was normal. Low fertility at the synchronized estrus resulted in development of alternative treatment practices, which combined feeding of MGA with injections or implants of estradiol-17β estradiol cypionate, luteinizing hormone, human chorionic gonadotropin, pregnant mare serum gonadotropin, or oxytocin. Estrus was synchronized after MGA and estradiol-17β or estradiol cypionate treatments, but fertility was low. Short-term feeding of MGA (5 to 7 d) combined with prostaglandin F2α or its analogs (PGF) on the last day of MGA reduced fertility at the synchronized estrus. The reduced conception at first service occurred in animals that began treatment after d 12 of the estrous cycle. However, feeding MGA for 14 d and then injecting PGF 17 d later avoided problems with reduced conception. Fertility of animals after this treatment was similar to that of contemporaries synchronized with Syncro-Mate-B. However, the length of the treatment period creates a need for increased management and may extend management beyond practical limits. Further research is warranted to address problems associated with reduced fertility after short-term treatment with MGA.
