The University of Arizona

Research Update

Feedlot/Calf Research Unit

FeedlotResearch continues to focus on nutritional management programs to improve performance and carcass characteristics of beef cattle. One graduate student (Clayton Bailey conducted two experiments: 1) evaluating effects of protein concentrations and gender on performance and carcass characteristics and 2) effects of ovarietcomization and Synovex-Plus implants on the somatotropic axis in feedlot heifers. These two studies have been presented in the Midwestern (gender based protein requirements) and Western (ovarietomization and implants) meetings of the American Society of Animal Science meetings in Des Moines, IA and Logan UT, respectively.

Evaluation of gender based protein requirements in feedlot cattle

-C.R. Bailey, G.C. Duff, S.R. Sanders, L.H. Baumgard, J.L. Treichel, and C.P. McMurphy
Department of Animal Sciences, University of Arizona

A study was conducted using a 2x3 factorial design, to ascertain the effects of three dietary protein concentrations on performance, carcass characteristics, and serum urea nitrogen (SUN) in finishing steers and heifers. Animals were blocked by gender and weight (three groups) and randomly assigned to receive a diet containing 11.0, 12.5 or 14.0% CP. Animals were weighed and bled at 28 d intervals for 84 d, overall daily DMI, ADG, and G:F were calculated and SUN was analyzed as a repeated measure throughout the study. Following slaughter, carcass data was collected for HCW, dressing percent (DP), KPH, 12th rib backfat (BF), LM area, marbling score (MS), and yield grade (YG). Heifers consumed less and gained less than steers (P < 0.01) and had lighter HCW (P < 0.01), less KPH (P = 0.08), lower MS (P = 0.02) and YG (P < 0.01) and numerically had less BF (P = 0.15). Dry matter intake (P = 0.02), ADG (P = 0.05), HCW (P = 0.08), and YG (P = 0.09) increased quadratically with increasing dietary protein. Hot carcass weight (P = 0.02), BF (P = 0.04), LM area (P = 0.04) and YG (P = 0.09) increased linearly with increasing dietary protein. Gain:feed, DP, KPH and MS was not affected by dietary protein concentration and G:F, DP, and LM area did not differ between genders. We did however, observe a gender x dietary protein interaction (P = 0.01) for G:F with steers being the most efficient at 12.5% CP, while heifers were most efficient at 14.0% CP. This could be a reflection of the heifers' overall advantage in leanness. Gender had no effect on SUN concentrations, but SUN increased linearly (P < 0.01) dietary protein concentrations and both linearly (P < 0.01) and quadratically (P = 0.01) with respect to day. In conclusion, quadratic responses in DMI and ADG indicate that a dietary protein level of 12.5% is optimal for either steers or heifers during the finishing period.

Effects of ovariectomization and Synovex-Plus implants on the somatotropic axis in feedlot heifers

-C. R. Bailey*, G. C. Duff*, S. R. Sanders*, S. P. Cuneo*, C. P. McMurphy*, S. W. Limesand*, J. A. Marchello*, D. W. Schafer*, M. L. Rhoads*, and D. M. Hallford†
*Department of Animal Sciences, The University of Arizona, Tucson, 85721
†Department of Animal and Range Sciences, New Mexico State University, Las Cruces, 88003

A 2 x 2 factorial design was used to evaluate effects of ovariectomization (OVX) and implantantation (200 mg of trenbolone acetate and 28 mg of estradiol benzoate; Synovex-Plus) on performance, serum urea nitrogen (SUN), serum IGF-1 (SIGF), and mRNA expression of hepatic IGF-1 (HIGF), total growth hormone receptor (HGHR) and estrogen receptor-α (HERA) as well as pituitary growth hormone (GH), estrogen receptor-α (PERA) and growth hormone releasing factor receptor (GRFR) in feedlot heifers. Thirty-two British x Continental heifers were randomly assigned to one of two gender groups (OVX or INTACT) and then either a non-implanted control (CON) or to receive a Synovex-Plus implant (IMP) and fed a 90% concentrate steam-flaked corn based diet for 42 d. Liver biopsies were taken prior to OVX for baseline expression of HIGF, HGHR and HERA, which did not differ (P > 0.45). Blood and BW were taken on d 0, 28 and 42 and one heifer/pen was slaughtered on d 42 for liver and pituitary samples. Initial and final BW did not differ (P > 0.19) due to OVX or IMP. No gender x treatment interaction (P > 0.24) was observed for ADG or final BW. Neither OVX nor IMP affected ADG for the final 14 d of the feeding period (P > 0.48), but 28 (P = 0.03) and 42 d ADG (P = 0.02) are greater in IMP than CON. No two or three way interactions with d were observed for SUN (P > 0.26) and SUN was greater in CON heifers than in IMP heifers (P < 0.01), but gender had no effect (P = 0.31). Both IMP and OVX increased SIGF (P < 0.01) and a gender x treatment interaction (P < 0.01) was observed. Neither gender nor implant treatment affected HERA, HIGF, HGHR, GRFR, GH, or PERA (P > 0.06). Data indicate that reductions in performance of OVX heifers can be eliminated through the use of Synovex-Plus implants. This is likely due to the implant treatment related increase of SIGF, but the reason for this increase cannot be explained by mRNA expression of key somatotropic genes in the present study.

Another study was conducted to evaluate effects of Bovigro (a humic/fulvic acid) on performance and ruminal ammonia concentrations of beef steers. This study was conducted in partial fulfillment for graduate credit in AnS 565 - Advanced Nutrition and Management - Feedlot. Results are pending on these data. In addition, Mr. Casey McMurphy is conducting an experiment to evaluate the product on ruminal fermentation of Holstein steers. We are evaluating the product as a potential replacement of ionophores for “naturally” fed Holstein steers.

Based on our feedlot research, we can conclude that 12.5% crude protein is optimal for beef steers and heifers in the feedlot. Negative effects of ovarietomization of beef heifers can be eliminated through effective implant programs; however, it appears that these effects are not due to alterations in either liver or pituitary growth hormone or insulin-like growth factor.

Calf Research Unit

Holstein steers have become of great financial importance to feedyards in the desert southwest including Arizona and southern California. Their availability and uniformity and overall production have out weighed the potential deficits in carcass characteristics (smaller and elongated ribeye area, increase kidney, pelvic and heart fat, etc.) and increased maintenance costs. In Arizona alone, an estimated 275,000 Holstein steers are raised in beef production facilities. At the current price of $0.80/ lb, the live value of the animals is well over $262,000,000. With an additional $5.00 generated (Galyean and Duff, 2002) from allied industries (feed, slaughter house, retail), total value to the Arizona economy approaches $1.3 billion annually. Therefore, improving performance of Holstein steers has a tremendous impact on the beef cattle industry and economy in Arizona.

Van Amburgh et al. (2003) suggested that nutrition and management during the first few weeks of life has long-term impacts on animal productivity. Although research has been conducted evaluating nutritional effects on performance of Holstein calves, the majority of the research has been conducted using heifer calves. Therefore, the Holstein bull calf remains one of the most over-looked groups of animals.

In addition to general performance of the animals, health of the milk-fed calf remains a primary road block to profitability. Death losses alone can be as high as 15% (Ritchie Kennedy, Kennedy Achers, Casa Grande, AR; personal communication). However, estimate of morbidity of milk-fed Holstein calves is unobtainable. We know that health of beef animals during the receiving period has a negative impact on performance during finishing as well as a negative impact on carcass quality. Notwithstanding morbidity during the early stages of life, losses due to digestive disorders (acidosis and bloat) during the finishing phases impacts profits. Furthermore, Smith (1998) suggested that losses from digestive diseases are greater in Holstein steers. Therefore, research evaluating nutrition and management factors to decrease morbidity and mortality in Holstein cattle will impact the cattle feeding industry in Arizona.

One study has been conducted on effects of a direct-fed microbial on performance and digestive tract morphology of day-old Holstein steers. Forty-four calves were purchased from a single source and received in three loads. Calves were fed milk replacer from day 1 and a starter diet from day 3 to weaning on day 49. On day 49, ½ of the calves were slaughtered at the University of Arizona Meat Laboratory and digestive tract samples collected from the rumen, duodenum, and ileum. Digestive tract samples have been evaluated microscopically for ruminal papillae height and width, intestinal villi ht and width and crypt height. Results are currently being summarized by Ms. Karianne Dick as a thesis for fulfillment for her M.S. degree. A second study evaluating the same direct-fed microbial will be conducted utilizing a larger number of calves (approximately 300) and taking calves from day 1 through finishing.

Additional research will evaluate nutritional management during this critical time period.

References

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