Suckling Behavior of Calves with Dams V a R Y I N G in Milk Production 1

Two experiments were performed to test the hypothesis that suckling behavior of calves with similar growth potential varies depending on cows' level of estimated milk production and stage of lactation. Eleven mature cows, which varied in estimated 205-d milk production (996 to 2354 kg/205 d), nursing heifer calves of similar growth potential were used in Exp. 1. Suckling behavior of calves was observed for two 24-h periods at three stages of lactation (average of 52,104 and 167 d postpartum). Suckling frequency (suckling bouts/24 h) declined as milk production increased at 52 d of lactation (-.00382 bouts/kg milk) but was unrelated to milk production at later stages. Duration of suckling (minutes/suckling bout) increased with estimated level of milk production at all stages of lactation (~= .001556 min/kg milk). Total time suckling tended to increase as estimated level of milk production decreased at 52 d of lactation, but this component of suckling behavior was unaffected by milk level at later stages. Suckling frequency declined from 8.6 bouts/24 h at 52 d of lactation to 4.5 bouts/24 h at 167 d of lactation when averaged across all cows. Total minutes nursed/24 h declined in a similar manner (64 mini24 h to 44 mini24 h) between 52 and 167 d of lactation. Duration of each suckling bout did not change with stage. In the second experiment the relationship of suckling behavior to estimated milk production was evaluated at four early stages (average of 17, 38, 59 and 80 d postpartum) of lactation using 20 mature cows. Variation in estimated 205-d milk production (1,034 to 2,237 kg/205 d) and growth potential of calves was similar to that of cows used in Exp. 1. Duration of postpartum anestrus as estimated by progesterone detected in weekly blood samples and the interval from calving to first behavioral estrus were also evaluated. Frequency of suckling declined (-.00185 bouts/kg milk) as milk production level increased. Total minutes nursed was related to estimated level of milk production only at 17 d of lactation (-.02649 min/kg milk). As in Exp. 1, frequency of suckling declined (11.3 bouts/24 h at 17 d of lactation to 3.8 bouts/24 h at 80 d of lactatation) and total minutes nursed/24 h decreased (80 mini24 at 17 d to 42 mini24 h at 80 d) as lactation progressed. Again, duration was unaffected by stage of lactation. Length of postpartum anestrus at (days to first estrus) was unrelated to milk level and (or) components of suckling behavior in this study. Data from these experiments confirm earlier reports that suckling behavior in calves varies with level of milk production of cows and indicate that the pattern of nursing changes as the lactation period progresses. (