Relationship between level of milk production and estrous behavior of lactating dairy cows

Abstract The objective of this study was to determine if there is an association between level of milk production and duration of estrus as determined by standing activity recorded by a radiotelemetry system. Holstein cows ( n =267; 50 DIM) were fitted with a transmitter that allowed continuous recording of standing activity. Cows were housed in a free-stall barn and milked twice daily. Ovulation was confirmed for all estruses ( n =380). Average milk production for the 10 days before the day of estrus was used to classify cows as lower ( 2 ) concentrations were determined in a subset of cows ( n =71) on the day of estrus. Duration (6.2±0.5 h versus 10.9±0.7 h; P P =0.001), and standing time (21.7±1.3 s versus 28.2±1.9 s; P =0.007) were shorter for estruses from higher (46.4±0.4 kg/day; n =146) than lower producers (33.5±0.3 kg/day; n =177). Milk production was correlated with the duration of estrus ( r =−0.51; P n =323). Higher producers had lower E 2 concentrations than lower producers (6.8±0.5; n =31 versus 8.6±0.5 pg/ml; n =40; P =0.01) in spite of larger pre-ovulatory follicle diameter (18.6±0.3; n =31 versus 17.4±0.2 mm; n =40; P =0.004). Interestingly, E 2 concentrations were not correlated with diameter of the pre-ovulatory follicle ( r =−0.17; P =0.15) but milk production was correlated with both E 2 concentrations ( r =−0.57; P r =0.45; P 2 .