Effect of dry period heat stress and rumen protected choline on productivity of Holstein cows

Dry period heat stress significantly reduces milk yield in the subsequent lactation in cows. Altered methylation patterns in mammary tissues is associated with the decline in milk yield. We hypothesized that as a methyl donor, choline (RPC) supplementation reverses similar patterns of methylation and thus productivity in heat-stressed dams. Late-gestation Holstein cows (n = 51) housed in freestall barns were enrolled to either heat stress (HT, n = 12), HT with RPC (HTC, n = 11), cooling (CL, n = 14), or CL with RPC (CLC, n = 14). A cooling system including shade, fans, and soakers was provided to CL and CLC cows, whereas HT and HTC cows only had shade. Choline treatment consisted of 30 g of RPC per day mixed with TMR. Dry matter intake (DMI), rectal temperature (RT), and respiration rate (RR) were assessed in the dry period (DP), and milk yield was tracked for 60 DIM. Statistical analyses were performed using the PROC MIXED procedure of SAS. HT+HTC increased RR and RT (78.7 ± 2.3 vs. 61.7 ± 1.9 bpm; 39.3 ± 0.07 vs. 38.8 ± 0.05°C; P < 0.01) relative to CL+CLC. HT exposure reduced DMI relative to CL (13.2 ± 0.4 vs. 14.4 ± 0.3 kg/d; P = 0.01). DMI of HTC cows was lower relative to HT (12.4 ± 0.4 vs. 13.8 ± 0.4 kg/d; P = 0.02). Gestation length (GL) was shorter in HT (HT+HTC; 271.2 ± 0.5) versus CL (CL+CLC; 274.9 ± 0.5 d; P < 0.01). HTC had a shorter GL and DP compared with HT (268.6 ± 0.9 vs. 273.6 ± 0.8 d; 38.6 ± 1 vs. 43.2 ± 0.9 d; P < 0.01), whereas CLC had a longer GL and DP than CL (275.8 ± 0.6 vs. 273.9 ± 0.6 d; 46.6 ± 0.6 vs. 43.9 ± 0.6 d; P = 0.03). Colostrum yield (P < 0.01) was lower in HT+HTC (7.4 ± 0.5 kg) relative to CL+CLC (11.5 ± 0.5 kg). Cooled calves (CL+CLC) were born heavier than heat-stressed (HT+HTC) calves (37.9 ± 0.4 vs. 33.3 ± 0.5; P < 0.01). HTC calves were born lighter than HS calves (31.7 ± 0.6 vs. 34.7 ± 0.6 kg; P < 0.01). In CL, ECM was increased compared with HT cows (54 ± 1.6 vs. 47.5 ± 1.7 kg/d; P < 0.01). An interaction of ECM yield was observed among treatments (P = 0.06): CL = 53, CLC = 54.9, HT = 47.9, and HTC = 47.1 kg/d. These results suggest that choline does not mitigate the negative impact of heat stress in prepartum cows but improves ECM yield when combined with cooling.

Key Words: dairy cattle, heat stress, choline