ABSTRACT
Dairy cattle are routinely managed in social groups and subject to various management and social transitions, yet conventional approaches to rearing dairy calves limit social experience during early weeks of life. The objective of this study was to evaluate long-term effects of dairy calf social housing, with calves housed individually or in pairs, on long-term behavioral responses observed in pregnant heifers following social regrouping and introduction to a novel housing environment. Holstein heifers were raised during the milk-feeding period (provided 8 L/d milk replacer) in either individual pens (n = 20 heifers) or paired pens (n = 20 pens; 1 focal heifer/pen) and subsequently identically managed in groups on pasture from 9 weeks of age. At 30 d before expected calving, pregnant heifers were moved from pasture to a free stall barn, which represented introduction to a novel social group and an unfamiliar housing environment. Behavior was continuously recorded from video for 24 h, beginning at 0000 h on the day after introduction, to characterize feeding behavior, locomotor activity, and stall usage, as well as social proximity and competitive behavior surrounding the feed bunk and stall. Stocking density of the free stall barn fluctuated and was categorized as low (≤75%, 100 × animals in pen/available stalls), medium (>75%, 100%), or high (≥100%). Body weights obtained following calving indicated that previously PH heifers were heavier (632.3 vs. 593.4 kg; PH vs. IH), and body weight was included as a covariate in analysis of feeding behavior. Upon introduction to the free stall pen, previously PH heifers spent more time walking (1.9 vs. 1.3 min/h) with no effect of calf social housing on duration of lying time. However, stall use was subject to an interaction between previous housing treatment and stocking density and differed overall between previous housing treatments; previously PH heifers spent less time in the stall, particularly at high stocking density (29.4 vs. 48 min/h), due to shorter (29.6 vs. 95.7 min/visit) but marginally more frequent stall visits. Previously pair-housed heifers were also less likely to be displaced from a stall (44 vs. 85% of heifers replaced; PH vs. IH). Feeding behavior was similarly influenced by previous housing treatment particularly at high stocking density, with previously PH heifers spending more time feeding (8.2 vs. 4.2 min/h) and visiting the feed bunk more frequently (1.5 vs. 0.8 visits/h). These results suggest that preweaning social housing had long-term effects on behavior and ability to adapt to a novel environment which became most apparent under heightened competitive pressure.