Effect of prebreeding body weight or progestin exposure before breeding on beef heifer performance through the second breeding season1

Programs for developing replacement heifers are designed for heifers to calve at 2 yr of age and to extend their stayability in the herd and minimize feed cost. The experimental objective was to determine whether developing prepubertal heifers on less dietary energy and to a BW of 55% rather than 65% of mature BW at 14 mo of age would compromise ovarian development and reduce fertility. In a 3-yr study, 8-mo-old Angus (n = 60/yr) and composite MARC II (n = 60/yr) heifers were assigned equally by age, BW, and breed to receive either a low (LG) or high (HG) BW gain diet fed to achieve an ADG of either 0.45 or 0.8 kg/d from 8 to 15 mo of age, including the first 21 d of breeding, and then transferred to pasture. At 14 mo, heifers were housed with fertile bulls for 47 d. Estrus was monitored for 21 d. Within 12 h after detection of estrus, ovarian length and height, preovulatory follicle diam., and antral follicle count (AFC) were measured by transrectal ultrasonography. Corpus luteum (CL) volume and plasma progesterone concentration were measured 5 to 15 d after estrus. Data were analyzed by ANOVA with treatment, breed, and year and their 2-way interactions as independent variables. At breeding, HG heifers were heavier than LG heifers (419.9 vs.361.8 ± 7.5 kg; P < 0.01); ADG for the treatment period was 0.79 vs. 0.47 ± 0.04 kg/d (P < 0.01), respectively. In 2010 and 2011, 97.2% of heifers were cyclic by 21 d of breeding. Size of the ovary, preovulatory follicle, CL, and AFC did not differ between HG and LG, but preovulatory follicle diam. and ovarian length were greater (P ≤ 0.05) for MARC II vs. Angus heifers. Progesterone concentrations were less for LG vs. HG heifers (P ≤ 0.02), whereas CL volume was not affected by treatment or breed but was correlated positively with preovulatory follicle size (P < 0.01). Total AFC ranged from 5 to 49 and was correlated positively with ovarian volume but was not associated with fertility. A greater proportion of HG vs.LG heifers conceived within the first 21 d of the breeding period (64.4% vs. 49.2% ± 3.8%, respectively; P < 0.01), but overall pregnancy rate was not affected by treatment (83.0% vs. 77.7% ± 3.1%, respectively; P > 0.10). Pregnancy rate was 10% less (P < 0.01) for Angus vs. MARC II heifers. Developing beef heifers at a lesser ADG to a lighter BW (55% vs. 64% of mature BW) at breeding did not influence postweaning ovarian development or AFC or compromise pregnancy rate during the 47-d breeding period.

Section: Discussionsupporting

confidence: 81%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effect of postweaning diet on ovarian development and fertility in replacement beef heifers1

Eborn

Cushman

Echternkamp

2013

“…Feeding replacement heifers to traditional target BW increased development costs relative to development systems where heifers were developed to lighter target BW ranging from 51 to 57% of mature BW (Funston and Deutscher, 2004;Roberts et al, 2007Roberts et al, , 2009Martin et al, 2008;Larson et al, 2009). Feeding to prebreeding BW as light as 51% of mature BW was shown to be more cost effective than development to 57% of mature BW (Martin et al, 2008). Previous research on decreased ADG heifer development has been conducted completely in the dry lot (DL), under controlled conditions.…”

Section: Introductionmentioning

confidence: 99%

Heifer development systems: Dry-lot feeding compared with grazing dormant winter forage1

Funston

Larson

2011

Self Cite

Two hundred ninety-nine Angusbased, nulliparous heifers (253 ± 2 kg initial BW) from 3 production years were utilized to compare traditional postweaning dry lot (DL) development with a more extensive winter grazing system utilizing a combination of corn residue and winter range (EXT). Heifers developed in the DL were offered a common diet after the weaning period for 208 d in yr 1, 194 d in yr 2, and 150 d in yr 3 until breeding. Heifers developed in EXT grazed corn residue for 135 d in yr 1, 106 d in yr 2, and 91 d in yr 3, and then fed in the DL until breeding (yr 1) or grazed dormant winter grass for approximately 60 d before being fed in the DL (yr 2 and 3). All 3 years, heifers were estrus synchronized, with timed AI performed in yr 1. In yr 2 and 3, estrus was detected and those detected in estrus were artificially inseminated approximately 12 h later. Heifers were exposed to bulls 10 d after the last AI for 60 d while grazing summer pasture. During the winter grazing period, EXT heifers gained less (P = 0.01) BW than DL heifers and EXT heifers had lighter (P = 0.02) BW at breeding. Fewer (P < 0.01) EXT heifers reached puberty before breeding. Conception to AI was not different (P = 0.23); however, AI pregnancy rate tended (P = 0.08) to be less in EXT heifers. Final pregnancy rates were not different (P = 0.38) between treatment groups. Although EXT heifers had lighter (P = 0.02) BW at pregnancy diagnosis; however, they did compensate with greater (P = 0.05) ADG after breeding, resulting in similar (P = 0.22) precalving BW. Winter development system did not influence (P > 0.10) percentage of calving in the first 21 d, calf birth date, and calf birth BW, or dystocia score. Pregnancy rate after the second breeding season was not different (P = 0.56) between treatments. Heifer development using extended winter grazing reduced (P < 0.01) the cost of producing a pregnant heifer by $45 compared with DL.

“…Biological data used in this analysis was collected at the University of Nebraska-Lincoln, Gudmundsen Sandhills Laboratory, and represents 2 consecutive investigations (Funston and Deutscher, 2004;Martin et al, 2008), which are combined into a single data set (n = 500). Heifers from the earlier study were a composite breed of 25% Hereford, 25% Angus, 25% Simmental, and 25% Gelbviech.…”

Section: Methodsmentioning

confidence: 99%

Bioeconomic factors of beef heifer maturity to consider when establishing criteria to optimally select and/or retain herd replacements

Stockton¹,

Wilson

Feuz

et al. 2014

Self Cite

The online version of this article, along with updated information and services, is located on Cammack et al. (2009, p. 517) wrote, "Biological and economic efficiencies of cow-calf production are largely dependent on successful reproduction." The literature is replete with works about reproduction, dystocia, and maturity. Bellows et al. (1971) used ordinary least squares (OLS) regression to quantify the effect of physical size on 4 degrees of dystocia. Morrison et al. (1985) and Basarab et al. (1993) proposed using a discriminant analysis methodology. While similar to OLS, this method optimizes a different objective function giving the estimates of the coefficients an altered meaning and use. In seeking a method to optimize productivity and identify the control variables for reproduction efficiency, Greer et al. (1983) developed an "index of maturity." Their index values proved to be less than statistically significant. More recently, work by Patterson et al. (1992) using target weight (TW) has become a widely accepted method to forecast maturity and initiate heifer breeding. Using the same metric, Feuz (1991) developed a profit function. 4733 INTRODUCTIONAs Feuz (1991) recognized, the economically optimal breeding readiness of beef replacement heifers is that point of development where costs are less than or equal to expected revenues obtained by such development. Costs and revenues are dependent on both physical and economic factors used in producing beef cattle, and any model used to accurately reflect profitability/ productivity must include both. In a step toward this end, the maturity index (MI) developed by Stockton et al. (2013) ABSTRACT: Understanding the biology of heifer maturity and its relationship to calving difficulty and subsequent breeding success is a vital step in building a bioeconomic model to identify optimal production and profitability. A limited dependent variable probit model is used to quantify the responses among heifer maturities, measured by a maturity index (MI), on dystocia and second pregnancy. The MI account for heifer age, birth BW, prebreeding BW, nutrition level, and dam size and age and is found to be inversely related to dystocia occurrence. On average there is a 2.2% increase in the probability of dystocia with every 1 point drop in the MI between the MI scores of 50 and 70. Statistically, MI does not directly alter second pregnancy rate; however, dystocia does. The presence of dystocia reduced second pregnancy rates by 10.67%. Using the probability of dystocia predicted from the MI in the sample, it is found that on average, every 1 point increase in MI added 0.62% to the probability of the occurrence of second pregnancy over the range represented by the data. Relationships among MI, dystocia, and second pregnancy are nonlinear and exhibit diminishing marginal effects. These relationships indicate optimal production and profitability occur at varying maturities, which are altered by animal type, economic environment, production system, and management regime. With thes...