In the hot-weather regions, during the hottest hours of day, cattle experienced major difficulties dissipating excessive heat load to the environment. The main source of heat production of cattle is rumen fermentation process. Changing common feeding schedule from day to night hours could help cattle easily dissipate the heat from digestive process to surrounding and impact on its performance. With the objective of comparing once-per-night vs. traditional twice-a-day feed-delivering schedule on feedlot performance of back-growing cattle in hot climate, 80 bull-calves (244.9 kg BW) were involved in a 56 feedlot experiment, performed during summer of 2018 in Culiacan, Mexico. In a complete block design experiment in groups of five were placed in 16 ground pens (6 x 12 m), and inner each block pens were randomly assigned to two treatments: 1) Feeding twice a day at 0900 and 1530 hours (Control); and 2) Feeding once a day at 2000 hours (Night treatment). In animals fed ad libitum with a growing diet, body weight, dry matter intake, average daily gain, and feed efficiency were measured. Pen (five animals) was consider as the experimental unit (8 by treatment). Results were subject to ANOVA and P < 0.05 fitted to accept statistical difference. Across experiment, maximum and minimum temperature were 44.7 and 23.6 °C, respectively; and maximum and minimum THI were 95.99 and 73.07, respectively. Night feeding schedule increased (P < 0.01) in 5% final weight, 25% daily gain, 7% dry matter intake, and 17% feed efficiency (gain: feed ratio). Results suggest that feeding time has a strong influence on feedlot performance of cattle under hot weather. It is concludes that delivering feed during the night hours becomes as a viable feeding strategy to improve feedlot performance of cattle in hot climates.
A 2 x 2 factorial study was conducted to evaluate main and interaction effects of feeding amino acid complexed sources of Zn (Zn-AAC; 40 mg /kg DM from Availa® Zn; Zinpro Corp., Eden Prairie, MN) and Cr (chromium methionine; Cr-Met; 0.20 mg / kg DM from Availa® Cr; Zinpro Corp., Eden Prairie, MN) fed in combination or separately, compared to an iso-Zn level Control (CON) group that provided Zn from ZnSO4 (80 mg Zn∙kg-1DM) with no supplemental source of Cr. Treatments were replicated into 4 pens with 5 finishing Bos taurus x Bos indicus bullocks/pen (80 bullocks; BW= 421 kg). Treatment diets were initiated 28 d prior to starting zilpaterol hydrochloride (ZIL; 15 mg/kg BW) with ZIL fed daily for 33 d followed by a 4 d withdrawal before harvest. During the ZIL-feeding Zn-ACC x Cr-Met interactions were present for ADG and Gain:Feed (G:F) where Zn-ACC improved ADG (P≤ 0.05) and Cr-Met improved G:F vs. CON. Effects may have been mediated by differences in DM intake (DMI), where DMI was numerically increased by Zn-ACC and decreased (P ≤ 0.01) by Cr-Met. Overall, feeding Cr-Met moderated DMI and improved G:F (P ≤ 0.05). Measures of carcass composition were not affected by Zn-ACC or Cr-Met. Hot carcass weight was increased (P ≤ 0.05) by feeding Zn-ACC and tended to increase with Cr-Met. Daily carcass gain increased from feeding either Zn-ACC or Cr-Met during the ZIL phase and overall study. Feeding Zn-ACC was a primary driver during the ZIL period and overall trial for increasing growth rate, with little or no influence on DM intake while feeding Cr-Met moderated DM intake to improve dietary and energetic efficiency. Balancing the feeding levels of Zn-ACC and Cr-Met will be key to optimizing the overall biological response and net return.
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