Effect of OmniGen-AF® and heat stress during the dry period on subsequent performance of cows

Abstract Text: Heat stress in dairy cows during the dry period impairs milk production in the next lactation. Feeding OmniGen-AF® (OG) to lactating cows during heat stress increases dry matter intake (DMI), lowers respiration rate (RR) and rectal temperature (RT), but effects in dry cows are not known. We hypothesized that OG supplementation before, during and after the dry period (approximately 160 days) would overcome the effects of heat stress and improve performance.  Treatment groups were: heat stress (HT, only shade, n=17), heat stress with OmniGen-AF® (HTOG, 56 g/d, n=19), cooling (CL, shade, fans and sprinklers, n=16), and cooling with OmniGen-AF® (CLOG, n=11). Cows were randomly assigned to treatments based on previous mature equivalent milk production.  Cows were dried off 45 d before expected calving and after parturition; cows were kept under the same cooling system and management, until 60 DIM. Cooling cows during the dry period reduced RT (CL vs. HT; 38.8 vs 39.0, P < 0.01) and RR (CL vs. HT; 44 vs. 73, P < 0.01).  RR was also decreased by OG supplementation (OG vs. Non-OG; 56 vs. 61, P < 0.01). There was an interaction between OG supplementation and HT (P < 0.1); HTOG cows had lower RT compared to HT cows. During the dry-period, OG reduced DMI relative to non-OG cows (P < 0.1).  Calf birth weight was greater in calves from CL cows (CL vs. HT, P <0.01).  In cows, no differences in hematocrit, total protein and BCS among treatments were detected. Cows on CLOG had higher BW (kg) at parturition (CLOG, 794.9; CL, 746.8; HTOG, 762.9; HT, 720). Gestation length was approximately 4 d longer for CL cows compared with HT cows (P < 0.01). Cows on CLOG, CL and HTOG treatments produced more milk (5.2±1.9, 4.8±1.6 and 4.6±1.4 kg/d, respectively) than HT cows (35.9±1.5 kg/d). Body weight after parturition and DMI were evaluated up to 60 DIM and averaged DMI 19.4±0.7 kg/d, with no differences observed among treatments. These results confirm that exposure of dry cows to heat stress negatively impacts milk production in the subsequent lactation.  Active cooling of dry cows and OG supplementation can reduce the negative effects of heat stress in the dry period.

Keywords: cooling systems, heat stress, OmniGen-AF®.