Graduate Thesis Or Dissertation
 

The influence of cow age on grazing distribution and utilization of mountain riparian areas and adjacent uplands

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  • The objective of this study was to evaluate the influence of cow age on grazing distribution relative to mountain riparian areas. In each of two years, sixty cow-calf pairs were stratified by age into the following treatments: 1) thirty first calf heifers (442 kg, body condition score (BCS)=4.5), and 2) thirty mature cows (5-7 years of age; 569 kg, BCS=5.0). From late July to early September, treatments were randomly assigned to four pastures with treatments reversed in Year 2. Analysis of hourly cattle locations observed during 4-d periods early (d 15 to d 18) and late (d 36 to d 39 in Year 1; d 29 to d 32 in Year 2) during the grazing bout revealed a three-way interaction between cow age, time of day, and grazing bout (P<0.01). In the morning hours of the early grazing bout, mature cows distributed farther from the stream (P<0.10), and occupied the riparian vegetation type less (P<0.10) than first calf heifers. No differences (P>0.10) in distribution occurred between age classes from 1300 h until dark. Similarly, during the late grazing bout, no differences were observed (P>0.10) between the distribution of the age classes. While no difference (P=0.20) occurred between age classes in total minutes spent grazing, first calf heifers foraged longer during the morning and evening bouts (P<0.10). The forage utilization pattern and the fecal deposits within 1-m of the stream were not different (P>0.10) between age classes. While mature cows tended (P=0.17) to have higher dry matter intake (DMI), first calf heifers consumed more feed per unit of body weight (BW) (P=0.08). Though first calf heifers tended (P=0.13) to gain more BW, no differences occurred between age classes in BCS change (P=0.69), or calf average daily gain (ADG) (P=0.34). In summary, mature cows distributed farther from water and spent more time outside the riparian vegetation zones during the morning hours early (d 15 to d 18) in the trial compared to first calf heifers.
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