Two of the most important problems in high-yielding dairy goat farms are early and accurate pregnancy diagnosis and the appropriate dry off of lactating does before the next kidding. The hypothesis posits that it could be possible to identify pregnant does through maximum progesterone milk levels at any time during the pregnancy, and that there is an optimal time to apply a lactation inhibitor to help dry off lactating does. Therefore, 114 Murciano-Granadina breed goats were used, from which 74 goats were inseminated at week 20 of lactation and samples of milk from pregnant and non-pregnant goats were taken at two-week intervals. The average maximum progesterone milk levels were higher outside the natural breeding season (40° latitude) than in the breeding season (11.6 ± 1.13 vs. 8.6 ± 1.02 ng/mL), although the levels from pregnant and non-pregnant goats were similar (10.85 ± 1.3 vs. 9.74 ± 1.6 ng/mL), except in the case of pregnancy with four foetuses (12.5 ± 1.3 ng/mL). Milk yield at mating does not affect fertility until a value of at least 3250 mL/day. Pregnancy started to affect milk yield up to the +7th week and was 59.9% lower in the +10th week after mating, so the use of lactation inhibitors could be more effective from this latter week. In conclusion, the results show that it is not possible to detect gestation in goats reliably through the maximum concentration of progesterone in milk at any time during lactation, except in the case of goats gestating four foetuses, that the milk yield of goats at mating does not affect fertility until a value of at least 3250 mL/day, and that from the 10th week post-mating, the application of lactation inhibitors would be optimal.
Keywords: Murciano-Granadina breed; goat; milk; progesterone; reproduction.