The current study involved two experiments that were conducted at the Texas A&M AgriLife Research and Extension Center in Uvalde, TX (semi-arid environment) from 2006 to 2008. In experiment one, Bonsmara bulls ( n = 39; 20-24 mo of age) were joined with multiparous Bonsmara and Bonsmara-influenced females (n = 1013) during a 90-day breeding season in 2006, 2007, and 2008 to quantify the effects of a reduction in bull to female ratio on reproductive performance. Bulls were also placed with primiparous beef females ( n = 142). Bulls were allotted by selected physical traits, social rank, serving capacity, and seminal traits to one of two bull to female (BFR) treatments: Low (1:30-1:45; n = 10 pastures) or Conventional (1:16-1:26; n = 12 pastures) BFR. Pregnancy rate (P = 0.36), calving date (P = 0.24), and calving rate (P = 0.25) did not differ between Conventional and Low BFR treatments. The current experiment demonstrates that Low BFR can be utilized in breeding pastures of up to 2,090 ha without negatively affecting reproductive performance. In experiment two, Bonsmara heifers (3/4, 7/8, and full bloods) were exposed to Bonsmara bulls from April 15 to July 15 during each of the two years. Heifers were weighed, rectally palpated for pregnancy, and scored for BCS (1 thin - 9 fat) and frame score (1 short - 9 tall) in December (end of second trimester) during years 1 and 2. Heifers were stratified on expected calving date and randomly allotted to one of two levels of nutrition for the remainder of gestation. In year 1, heifers were allotted to range forage (n=31, low nutrition, LN) or to non-irrigated oat pasture (n=31, high nutrition, HN). In year 2, heifers were placed onto the same range environment as in year 1 (n=31, LN) or onto irrigated ryegrass pasture (n=31,HN). Heifers in the LN groups were supplemented with 20% CP cubes at the rate of 0.9 kg/heifer/day from January 2 until calving while HN heifers were not supplemented. Within 4 hr of birth, calves were weighed, and calf vigor and calving difficulty scores were recorded. Heifers were weighed within 72 hours of parturition. From treatment initiation through calving, HN heifers gained 48.6 kg whereas the LN females lost 15 kg. Twice as many HN heifers required major assistance at calving as compared to LN heifers. Calves born to the HN females weighed 3.7 kg more at birth than those born to LN females. These differences resulted in HN heifers having (P = 0.005) more calving difficulty than LN heifers (mean calving difficutly of 2.3 for HN and 1.6 for LN). The calves of the HN females were also less vigorous (P = 0.005) after birth than the calves from LN females (calf vigor score of 2.2 for HN and 3.3 for LN). Consequently, the level of nutrition during the third trimester of gestation can affect calving difficulty, calf vigor, and female weight.

The current study involved two experiments which were conducted at the Texas A&M Agricultural Research and Extension Center in Uvalde (semi-arid environment) from 2002 to 2004. In experiment one, Bonsmara bulls (n = 19; 20-24 mo of age) were joined with multiparous, crossbred females (n =586) for 90 d in 2003 and 2004. Bulls were allotted by selected physical traits, seminal traits, social rank, and serving capacity to one of two bull to female ratio (BFR) treatments: Conventional (1:21-1:29; n = 6 pastures) or Low (1:47-1:52; n = 2 pastures) BFR. Pregnancy rate (P = 0.33), calving rate (P = 0.26), and calving date (P = 0.22) did not differ between Conventional and Low BFR treatments. Post-breeding evaluation of bulls in 2002 (n = 16) indicated that social rank, but not seminal traits, was significantly correlated with pre-breeding values (P < 0.05). The current study demonstrates that Low BFR can be utilized in single- and multisire, 90-d breeding pastures of up to 2,090 ha without adversely affecting reproductive performance. In experiment two, yearling, one-half or three-quarter Bonsmara heifers (n = 106; 11-14 mo of age) were palpated per rectum and assigned a reproductive tract score (RTS) immediately prior to the beginning of the breeding season. Reproductive performance was measured in their two subsequent breeding years in order to estimate the value of the RTS system in extensively-managed, natural mating, 90-d breeding season programs. RTS was positively correlated (p < 0.01) with frame score (r = 0.25), age (r = 0.31), weaning weight (r = 0.47), and the weight of the heifer on the day of RTS exam (r = 0.56). The RTS means by dam parity also differed (P < 0.03). A lower (P < 0.01) percentage of females conceived during each of their first two breeding seasons for heifers of RTS 1 and 2 (65.2%) than for heifers of RTS 3, 4, and 5 (91.2%). Females with a RTS of 1 had a lower pregnancy rate over each of their first two breeding seasons, conceived later during their first breeding season, weaned lighter first calves, and remained lighter each year for fall body weight and body condition score than did heifers with RTS of 2 to 5 (P < 0.05). Collectively, the results of the current study indicate that heifers with a RTS of 1 immediately prior to a 90-d breeding season should be culled. Consideration should also be given to eliminating RTS 2 heifers, but further studies will be needed to confirm the potential economic advantage of this practice.