Sprinkle James E, Ellison Melinda J, Hall John B, Yelich Joel V, Willmore Carmen M, Brennan Jameson R
Department of Animal, Veterinary and Food Sciences, University of Idaho, Moscow, ID 83844, USA.
Nancy M. Cummings Research, Extension & Education Center, University of Idaho, Carmen, ID 83462, USA.
Transl Anim Sci. 2021 Apr 7;5(2):txab063. doi: 10.1093/tas/txab063. eCollection 2021 Apr.
The objectives were to determine if previously classified, efficient (LRFI, low-residual-feed intake, = 12 × 2 yr) vs. inefficient (HRFI, high-residual-feed intake, = 12 × 2 yr) lactating 2-yr-old Hereford × Angus cows differed in grazing behavior, body weight (BW), body condition score (BCS), and calf weaning weight while grazing rugged rangeland pastures. Cows were fitted with grazing halters containing both an accelerometer and a global positioning system (GPS) data logger during June 14 to July 4, 2016, August 2 to 25, 2016, May 23 to June 12, 2017, and August 5 to 28, 2017. GPS data were recorded at 7-min intervals in 2016 and 4-min intervals in 2017 and accelerometer data recorded at 25 times/s. Grazing time (GT), resting, walking, bite rate (BR), daily travel distance (DTD), elevation, and slope were analyzed with a mixed model that included fixed effects of RFI group, day, and RFI group × day and cow within treatment as the random effect. Cow BW, BCS, and calf weaning weight were analyzed by analysis of variance with treatment as the main effect. There were no differences ( > 0.10) due to RFI detected for BW, BCS, or calf weaning weights. During periods of mild heat load (MHL), HRFI cows spent more ( < 0.05) time resting during the day at lower elevations ( < 0.05) than LRFI cows. During a 6-d period in spring with only 2 h MHL, HRFI cows grazed 1.7 h/d longer than LRFI cows ( < 0.05); commencing grazing earlier in the morning and extending the grazing bout later. During the summer with > MHL, LRFI cows grazed more than HRFI cows 18% of the time ( < 0.10). The HRFI cows had greater GT than LRFI cows only 3% of the time ( < 0.10) during summer. There was no difference ( > 0.10) in BR between HRFI and LRFI cattle. The DTD tended ( < 0.10) to be greater for LRFI cattle during summer 2017. Over all sample periods, HRFI had greater walking than LRFI 15% of the time and LRFI exceeded HRFI cattle for walking 3% of the time ( < 0.10). The greater walking for HRFI was assumed to be associated with more search grazing. Metabolic heat load on hot summer days for HRFI cattle is presumed to have contributed to differences observed in grazing behavior. These results suggest that lactating cows with low-RFI phenotypes appear to be better adapted to grazing rugged rangelands in late summer during periods of MHL.
本研究的目的是确定先前分类的高效（低剩余采食量，LRFI，n = 12×2年）与低效（高剩余采食量，HRFI，n = 12×2年）的两岁哺乳期赫里福德×安格斯奶牛在崎岖的牧场放牧时，其放牧行为、体重（BW）、体况评分（BCS）和犊牛断奶体重是否存在差异。在2016年6月14日至7月4日、2016年8月2日至25日、2017年5月23日至6月12日以及2017年8月5日至28日期间，给奶牛佩戴装有加速度计和全球定位系统（GPS）数据记录器的放牧颈圈。2016年GPS数据以7分钟间隔记录，2017年以4分钟间隔记录，加速度计数据以每秒25次的频率记录。采用混合模型分析放牧时间（GT）、休息、行走、咬食率（BR）、每日行进距离（DTD）、海拔和坡度，该模型包括RFI组、日期以及RFI组×日期的固定效应，并将处理内的奶牛作为随机效应。通过以处理为主要效应的方差分析来分析奶牛的BW、BCS和犊牛断奶体重。在BW、BCS或犊牛断奶体重方面，未检测到因RFI导致的差异（P>0.10）。在轻度热负荷（MHL）期间，HRFI奶牛在白天较低海拔处休息的时间比LRFI奶牛更多（P<0.05）。在春季为期6天且仅存在2小时MHL的时间段内，HRFI奶牛每天的放牧时间比LRFI奶牛长1.7小时（P<0.05）；它们更早开始放牧，并延长放牧时间。在夏季MHL>期间，LRFI奶牛放牧时间超过HRFI奶牛的时间占比为18%（P<0.10）。在夏季，HRFI奶牛的GT仅在3%的时间内大于LRFI奶牛（P<0.10）。HRFI和LRFI牛之间的BR没有差异（P>0.10）。在2017年夏季，LRFI牛的DTD有增大的趋势（P<0.10）。在所有采样期内，HRFI牛行走时间超过LRFI牛的时间占比为15%，而LRFI牛行走时间超过HRFI牛的时间占比为3%（P<0.10）。HRFI牛行走较多被认为与更多的搜索式放牧有关。推测炎热夏日HRFI牛的代谢热负荷是导致观察到的放牧行为差异的原因。这些结果表明，具有低RFI表型的哺乳期奶牛似乎在夏季后期MHL期间更能适应在崎岖牧场放牧。
