Effects of Supplement Type on Growth and Pregnancy Rate of Yearling Brahman-Crossbred Heifers1

Professional Animal Scientist, Jun 2004 by Arthington, J D, Lamb, G C, Pate, F M

Abstract

The effects of winter supplement type on growth and pregnancy rate of fall-born, yearling heifers was investigated over 2 consecutive yr. During both years, heifers were stratified by breed (Braford and Brangus-crossbred) and BW and randomly assigned to one of two treatments consisting of 1) wheat middling-based range cube or 2) molasses-cottonseed meal slurry (n = 34 and 24 heifers per treatment for yr 1 and 2, respectively). Supplements were fed at rates to achieve a target of 1.47 and 0.34 kg of supplemental TDN and CP daily, respectively. Four limpograss (Hemarthria altissima) pastures were utilized each year (n = 2 pastures per treatment; 0.71 and 0.51 ha per heifer for yr 1 and 2, respectively). All heifers were allowed free-choice access to stargrass (Cynodon nlemfuensis) hay during periods of limited pasture forage availability. During a 70-d breeding season, heifers were combined by group and exposed to mature Angus bulls. Bulls were rotated among pastures each week. Individual heifer BW and hip height were collected at the start of supplementation and at the start and end of the breeding season. Pregnancy rate was determined by transrectal ultrasonography in late April of each year (minimum of 40 d after the end of breeding). There were no treatment � year, breed � treatment, or breed � year interactions for heifer ADG (P>0.10). Supplement type did not affect heifer ADG (0.44 and 0.47 kg/d for molasses-slurry and range cubes, respectively). Heifers consuming molasses-slurry had a greater (P

(Key Words: Heifer, Molasses, Wheat Middlings, Pregnancy.)

Introduction

The nutritional considerations for heifer development are an important component in a cow-calf production system (Bagley, 1993). Heifers must be placed on a high plane of nutrition to achieve puberty soon enough so that they may conceive at 14 to 15 mo of age (Short and Bellows, 1971). Further, heifers with Brahman breeding influence tend to mature more slowly and attain puberty at an older age (Martin et al., 1992). Tor beef producers in the southeast and Gulf Coast region of the US, the influence of Brahman breeding may restrict the ability for producers to breed heifers as yearlings to calve at 2 yr of age. In these situations, the impacts of supplemental nutrition are increasingly important to heifer development systems. In Florida, as well as other regions of the Gulf Coast, beef cattle producers have options of molasses-based vs dry-feed supplement sources. Decisions for the use of these products are often based on issues of convenience and cost per unit of nutrient delivered. The objective of this study was to compare the effects of equal amounts of TDN and CP delivered through 1) molasses-cottonseed meal slurry or 2) wheat middling-based range cubes on growth and reproductive performance in Brahman-influenced yearling heifers.

Materials and Methods

This study was conducted at the University of Florida-IFAS, Range Cattle Research and Education Center located in southwest Florida. The weather conditions at this location are considered tropical-subtropical. The animals utilized in these experiments were cared for by acceptable practices as outlined in the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching (FASS, 1999).

This study was conducted over 2 consecutive yr (2002 and 2003) using a total of 116 heifers. The heifers were derived from two cowherds maintained at the Range Cattle Research and Education Center consisting of either Braford or Brangus-crossbred breeding, both having approximately 38% Brahman influence. Heifers were born over a 90-d calving season beginning in October of the previous year. Heifers were weaned during the first week of August in both years. The trial began on November 9 and September 4 in yr 1 and 2, respectively, and heifer age at the start of the study did not differ (R>0.40) (376 and 375 and 297 and 307 d of age for yr 1 and 2, respectively). Heifers were stratified by breed and initial BW (255 and 266 kg for yr 1 and 2, respectively) and randomly allocated to four pastures (12.2 and 6.1 ha per pasture for yr 1 and 2, respectively) of established Floralta limpograss (Hemarthria altissima; n = 17 and 12 heifers per pasture for yr 1 and 2, respectively). Supplement treatments were randomly assigned to pasture and were designed to provide 1.47 and 0.34 kg/d of TDN and CP either through 1) molasses-cottonseed meal slurry or 2) wheat middlings-based range cube (Table 1). Supplements were fed three times weekly [6.35 and 5.56 kg per head at each of three feedings; Monday, Wednesday, and Friday (as-fed basis) for molasses slurry and range cubes, respectively]. The moisture content of each supplement was 77.5 and 88.0% for molasses-cottonseed meal slurry and wheat middlings-based range cube, respectively. Heifers were provided free-choice access to long-stem stargrass (Cynodon nlemfiiensis) hay (11.2 and 53.8% CP and TDN, respectively; DM basis) during months when pasture forage was limiting (beginning in December of each year). This typically coincides with the date of the first frost for our region. Heifers were provided free-choice access to a complete salt-based trace mineral supplement, which contained 12% Ca, 12% P, 7.8% Na, 0.18% Zn, 0.10% Mn, 699 ppm of Cu, and 89 ppm of Co.

Heifers were exposed to mature Angus bulls for 70 d beginning on December 3 and December 19 for yr 1 and 2, respectively. Bulls were rotated among pastures each week. During the breeding season, heifer pastures were combined within treatment such that there was one group per supplement treatment. Heifer BW (following a 12-h shrink) and hip height were collected at the start of the study and at the start and end of the breeding season. Heifer pregnancy status was confirmed by transrectal ultrasonography (5.0-mHz intrarectal transducer; Aloka� 500V; Corometrics, Wallingford, CT) in April of each year. The study was concluded at the end of the breeding season each year.

Random samples of supplement and hay were collected throughout the trial in both years. Samples were composited within year and assayed in duplicate for nutrient content at a commercial laboratory (SDK Laboratories, Hutch inson, KS). Total digestible nutrient values were estimated using in vitro OM digestibility (IVOMD) results: [(0.49 � IVOMD) + 32.2] � 0.93. Nutrient content of limpograss pasture was not analyzed; however, pasture forage availability and access to hay appeared similar across all pastures. Heifers were rotated among all pastures every 7 to 10 d so that each treatment group had equal access to all pastures.

Statistical analysis of BW and hip height was achieved by ANOVA for a completely randomized design using PROC MIXED of SAS� (SAS Inst. Inc., Cary, NC). The model statement contained the effects of treatment and breed and the interaction for treatment � breed. Data were analyzed using the pasture � treatment interaction as random effects. Breed group within pasture was the experimental unit. Analysis of heifer pregnancy rate was achieved by comparing heifer breed and treatment with pregnancy rate using PROC FREQ of SAS. Differences in pregnancy rate were compared using Chi-square analysis.