A study was designed to evaluate estrus response and fertility after treatment with melengestrol acetate (MGA) and prostaglandin F2 alpha (PGF2 alpha) in yearling beef heifers. Three hundred four heifers at three locations were allotted to one of two treatments: Treatment 1 served as a nonsynchronized control (CON); and heifers in Treatment 2 received .5 mg of MGA.animal-1.d-1 for 14 d and 25 mg of prostaglandin F2 alpha (PGF2 alpha) 17 d after MGA (MGA-PGF). Heifers in CON and MGA-PGF groups were artificially inseminated 12 h after observed estrus for 21 and 6 d after PGF2 alpha, respectively. Blood samples were collected from each heifer 10 d before and on the day MGA feeding began and 10 d before and on the day PGF2 alpha was administered. Heifers with concentrations of serum progesterone greater than 1 ng/mL on either date before administration of MGA or PGF2 alpha were considered pubertal. More (P = .02) prepubertal heifers that received MGA attained puberty by initiation of breeding than did CON heifers (72 vs 45%, respectively). The proportion of heifers that displayed estrus within 6 d after PGF2 alpha was greater (P less than .001) for MGA-PGF than for CON heifers (77 vs 25%, respectively) but was also influenced by location (P = .03). Conception rate at first service for MGA-PGF heifers that attained puberty during MGA feeding and before PGF2 alpha was not different (P = .50) from that of CON that attained puberty during the same period.(ABSTRACT TRUNCATED AT 250 WORDS)
In 1994, 1995, and 1996, a commercial heifer development operation purchased a total of 1542 potential replacement heifers. Heifers were purchased in the fall proceeding the spring breeding season and fed a silage-based diet during the developmental period. Before the breeding season began, heifers that failed to meet minimum requirements for pelvic area, average daily gain, body weight, disposition, or structural soundness were culled. During the first year, 42% of 483 heifers were culled, 17% of 468 heifers were culled in the second year, and 14% of 591 heifers in the third year. Estrus was synchronized and heifers were inseminated artificially (AI) for 30 days followed by 30 days of natural mating by cleanup bulls. First-service AI conception rates averaged 68% and overall pregnancy rates (AI + natural mating) averaged 95.1% over the 3-year period. Heifers culled prior to the breeding season realized a net profit of $9 per head, whereas heifers diagnosed nonpregnant after the breeding season lost $86, and heifers that aborted lost $133. Profits for pregnant heifers sold were $163 for first-service AI, $138 for second-service AI, and $83 for bull bred.
At the KSU Purebred Unit, 164 purebred Angus, Hereford, and Simmental cows were used to test a new estrus-synchronization program using GnRH, PGF2, and norgestomet. Cows were inseminated after detected estrus, or in the absence of estrus, inseminations were made at one fixed time after a second injection of GnRH. The treatment consisted of a 100 µg injection of GnRH plus a 6-mg ear implant of norgestomet. Seven days later, the ear implant was removed, and 25-mg of PG F2% was injected. In the absence of estrus, the time-bred group received a second injection of GnRH 48 h after PGF2% and was inseminated 16 h later. The treatment induced 10 of 36 anestrous cows to ovulate. Conception rates tended (P<.09) to be greater in Angus (72.2%) than Hereford cows (52.8%) , with conception rates in Simmental cows (51.5%) being similar to those in Hereford. Overall, pregnancy rates were similar between the time-bred group (59.3%) and the estrus-bred group (53.8%). We conclude that using GnRH, PG F2%, and norgestomet in a timed breeding program ca n eliminate the necessity of heat detection. In addition, the treatment induced estrus in 28% of the noncycling cows.
Abstract Beef heifers (374) were utilized to determine if zeranol implantation would influence pelvic development, dystocia and conception rates. One hundred fortyseven spring-born Simmental (SS) and 135 fallborn Angus (AF) heifers were allotted to two treatments: 1) controls (C); and 2) single zeranol implant at weaning (W). Ninety two fall-born Simmental (SF) heifers were allotted to three treatments: 1) C; 2) W and 3) single zeranol implant preweaning (PW) at 2 mo of age. Birth weights and weaning (200 d), yearling (360 d) and prepartum (700 d) weights and pelvic areas were measured. PW improved ( P P 2 ; 195 vs 188 cm 2 ; and 175 vs 168 cm 2 ; for SF, SS and AF, respectively). Prepartum pelvic areas were larger ( P
A total of 6,618 calves fed at eight Iowa feedlots were used to evaluate the effect of postweaning health on feedlot gain and carcass quality grade. The calves, representing 12 states, were consigned to the Iowa Tri-County Steer Carcass Futurity and were weighed upon arrival, after 35 days, at reimplant, and prior to harvest. A common dietary energy level was utilized at each feedlot. Calf health was classified as no treatment (NT; N=5,500), single treatment (ST; N=575), or two or more treatments (2T; N=543). The predominant cause of treatment was respiratory problems. Calves were sorted and harvested when they were visually evaluated to have 0.4 inches of fat cover. Feedlot ADG was 3.06, 2.93, and 2.87 lb/day for the NT, ST, and 2T calves, respectively. Calf sex, origin of calf (Southeast vs. Midwest), season of delivery (fall vs. spring), and color (black vs. red vs. white) all affected feedlot gain. The percent USDA Prime, Choice, Select, and standard for NT, ST, and 2T calf carcasses were 1.87, 70.3, 25.3, and 2.6; 1.05, 62.9, 30.1, and 5.9; and 0.9, 57.9, 30.6, and 10.6, respectively. A total of 4,499 calves were Angus-type calves eligible for Certified Angus Beef® (CAB®) acceptance. CAB® acceptance percentages for NT, ST, and 2T carcasses were 27.1, 24.2, and 18.7, respectively. CAB®acceptance rates were also impacted by calf sex (steers = 14.7% vs. heifers = 23.7%) and season of feedlot delivery (spring = 14.5% vs. fall/winter = 23.8%). Calves treated two or more times upon feedlot arrival had reduced feedlot gain, reduced quality grade, and reduced CAB® acceptance rate compared to untreated calves.
Heifers developed on high-endophyte, tall fescue gained half as much weight (56 vs 117 lb; P<.01) and had a lower 35-day pregnancy rate (15 vs 58%; P<.01) compared to heifers fed low endophyte, tall fescue. Based on progesterone serum concentrations and visual determination of estrus, the proportion of heifers that had attained puberty by the start of the breeding season tended (P=.11) to be greater when fed oxytetracycline (55 vs 68%).
When you evaluate the factors influencing profitability in the cow/calf industry, four key points need to be considered.1. Percent cows weaning calves.2. Weaning weight of calves.3. Selling price of calves.4. Annual cost of maintaining the cow.
Obviously, in evaluating weaning weight, it's important to consider both the percent of cows weaning calves and the actual weaning weight. If the goal is to improve weaning weight it cannot be at the expense of a dramatically reducing percent calf crop. The relationship of these two key profit factors is illustrated clearly in Table 1. Thus, in evaluating weaning weight it's important to look at weaning weight as actual pounds of calf weaned per cow in the herd.
In the past 20 years, it is very clear that the cow/calf industry has made considerable progress in improving calf weaning weights. The pounds of calf produced per cow nationally, (figures as summarized by Cattle Facts) were 318 lbs calf/cow in 1960, 449 lbs calf/cow in 1980 and current figures in 1989/90 are projecting 528 lbs calf/cow.
As we evaluate annual cost of maintaining the cow, very little change has occurred in the industry in the past ten years, but the current focus, such as the National IRM Program, will be addressing production costs and how the industry can improve economic efficiency by lowering annual production costs.
The following summary will look at those factors such as management, nutrition and genetics that can influence weaning weight.
Seven factors (in varying detail) will be considered: a) growth promotants, b) creep feeding, c) use of medicated minerals, d) internal/external parasite control, e) age at weaning, f) grazing systems/forage quality and g) genetic capacity to grow.
