Effects of cysteamine on performances of late--lactating cows during hot summer

Objective: To investigate the effects of cysteamine compound (Lactonin) on milk production of late-lactating cows during hot summer when the temperature humidity index (THI) was higher than 76 and cows were suffered from heat stress.

Methods: In this experiment 96 black and white dairy cows, based on milk yield (M) prior to the experiment, were assigned into 4 groups (G): G1 (M < 24 kg/d), G2 (24 < M< 28 kg/d), G3 (28 < M < 32 kg/d) and G4 (M > 32 kg/d). Each group (n = 24) was further divided into subgroups of Lactonin (3000 U/d) treatment (LT, n = 49) and control (n = 47).

Results: In G1 of LT, the rectal temperature decreased (P < 0.05), milk yield, fat-corrected milk, milk fat and feed conversion rate (FCR) increased (P < 0.05). These were companied with trendy of higher milk protein and lower somatic cell count. With whole LT cows (n = 49), the mean milk fat (%) increased (P < 0.05), mean milk protein tended to increase, and the mean milk yield and FCM tended to be enhanced. Plasma T3, T4 tended to decline whereas insulin enhanced (P < 0.01) significantly in LT herd (n = 49).

Conclusions: Lactonin helps heat-stressed cow to maintain a more normal metabolism in hot summer. This positive effect of Lactonin on cow performance is associated with Lactonin-dependent alteration of plasma insulin, T3 and T4.