Production, Management, and the Environment 3

摘要

We hypothesized that late-gestation hyperthermia impairs performanceof daughters and granddaughters of dams heat stressed when dry. To testthis hypothesis, we used lactation records from experiments conductedduring 10 summers at the University of Florida (2008–2018; THI >68). A total of 158 daughters (F1; CL_(F1) n = 78, HTF1 n = 80) and 45granddaughters (F2; CL_(F2) n = 24, HTF2 n = 21) of multiparous damsthat were actively cooled (CL, shade, fans and soakers, n = 78) or not(HT, shade only, n = 80) during a 46-d dry period were used. Milk yield,fat and protein records of the F1 and F2 were used to estimate energycorrected milk (ECM), and life events were also assessed (i.e., cullingand longevity). We evaluated ECM from calving to 35 weeks in milk(WIM) for 3 consecutive lactations. Data were analyzed using MIXEDprocedure of SAS with HT or CL, WIM (repeated measure) and theirinteraction as fixed effects, and dam(treatment) as random effect. Cullingpercentage before breeding was analyzed by Chi-squared contingencytest using FREQ procedure of SAS. In this regard, 30% of HTF1 wereculled before breeding, whereas 18% CL_(F1) were culled before breeding(P = 0.07). The longevity of HTF1 was 32% lower than CL_(F1) (2.53 vs.3.35 ± 0.34 yr respectively; P = 0.02). Moreover, HTF1 produced lessECM milk than CL_(F1) in their first (29.2 vs. 31.6 ± 0.07 kg, respectively;P < 0.01), second (36.2 vs. 34.3 ± 0.11 kg, respectively; P < 0.01) andthird lactations (40.1 vs. 33.4 ± 0.19 kg, respectively; P < 0.01). Theprobability of culling before breeding (CL_(F2) = 16.7 vs. HTF2 = 38.1%;P = 0.11) and longevity (CL_(F2) = 3.13 and HTF2 = 2.16 ± 0.48 years;P = 0.16) was similar between CL_(F2) and HTF2. Granddaughters bornto HTF1 produced less ECM milk than granddaughters born to CL_(F1) intheir first (HTF2 = 29.1 vs. CL_(F2) = 32.8 ± 0.12 kg; P < 0.01) and secondlactations (HTF2 = 35.3 vs. CL_(F2) = 40.0 ± 0.29 kg; P < 0.01). Dry periodheat stress exerts transgenerational effects on at least 2 generations and2 lactations of daughters and granddaughters that never experienced HTnor CL treatments directly.