Environmental conditions affecting mothers during pregnancy may modify the fetal programming through physiological and epigenetic changes. This study aimed to evaluate the postnatal effects of heat stress (HS) during early pregnancy on dairy goats. Thirty lactating Murciano-Granadina dairy goats (41.8 ± 5.7 kg BW) in late lactation were housed in pens of 5 and synchronized with vaginal sponges to be mated naturally at 2-d intervals. Goats were allocated to 2 balanced groups to which thermoneutral (TN, n = 15; 15–20°C) or HS (n = 15; 12-h day at 37 ± 0.5°C, 12-h night at 30 ± 0.5°C) conditions were applied before (d −12 to 0) and after fertile mating (d 1 to 45). Does were fed a total mixed ration (70% alfalfa hay and 30% concentrate) ad libitum and water was freely available. Rectal temperature and respiration rate were recorded 3-d per week at 8, 12 and 17 h. Feed and water intake were recorded daily. From d 45 onwards of pregnancy all the goats were joined in a unique group and conducted under semi-intensive conditions. Two weeks before the expected parturition, does were weighed and moved to kidding pens for permanent supervision. At delivery, litter size, pregnancy length and litter weight were recorded. Kids were fed with a milk replacer ad libitum and weighed at d 35 of age. Data were analyzed by PROC MIXED for repeated measurements of SAS (v.9.1.3). Table 1 summarizes the obtained results (RMSE, residual mean square error). Although litter size did not vary by treatment, pregnancy length was shorter (−3 d) in HS than TN does and, consequently, birth weight of the kids tended to be 7% lower in the HS group (P < 0.10). Neither growth until d 35 nor body weight of 35-d-old kids were affected by the treatments. In conclusion, a short period of HS (i.e., heat wave) during the mating period and early pregnancy will reduce the duration of pregnancy with possible epigenetic effects on the kids. Further research is needed to know the long-term effects produced by fetal programming on the kids. Study supported by MINECO Spain (Project AGL2013–44061-R). Table 1.

Item	TN	HS	RMSE	P-value
Treatment	Litter size
Litter size, no. kids	2.31	2.23	0.79	0.806	—
Litter weight, kg	5.40	4.71	0.71	0.061	0.001
Pregnancy length, d	146	143	2	0.006	0.915
Kid birth weight, kg	2.34	2.18	0.38	0.122	—
Kid weaning weight d-35, kg	7.88	7.64	1.34	0.520	—