Effects of nutritional grouping on productive performance and culling rate and its ‎causes in dairy herd

The aim of the present study was to investigate the effect of single nutritional grouping (TMR1) compared to multinutritional grouping (TMR4) on productive performance and milk composition during a complete lactation period. Four hundred and eighty-four lactating Holstein cows were blocked based on parity (158 first, 134 second, and 192 third lactation or higher) and were randomly assigned one of two TMR1 and TMR4. Cows in 1TMR produced 4.04 kg more milk than those in 4TMR group (P<0.01). Likewise, 4% FCM yield was higher for 1TMR relative to 4TMR (37.46 vs. 33.1 kg, respectively). The content of milk compositions were not affected by experimental treatments (P> 0.05). According to the results of milk production, fat (P<0.01) and protein milk yields (P<0.01) were higher for TMR1 compared to TMR4. Cows in 4TMR were culled 1.58 times compared to those in 1TMR during lactating period. (CI95%= 1.01-2.46; P= 0.04).