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Summary Embryo and early foetal development was studied until Day 60 (ovulation = Day 0) in 25 Brazilian jenny donkeys. The occurrence of ovulation and embryonic development was assessed by daily examinations using realtime ultrasonography. An embryonic vesicle, first detected at Day 10.9 ± 0.1 after ovulation, remained mobile within the uterine lumen until Day 16.0 ± 0.5 when it had a diameter of 21.8 ± 1.5 mm. Until immobilised the vesicle was detected in the left horn, right horn and body of the uterus 49.2, 41.8 and 9% of the time respectively. There was a temporal relationship between vesicle expansion, increase in uterine tone and immobilisation of the vesicle. The mean diameter of the embryonic vesicle or conceptus was 3.5, 28.0, 30.9, 45.3 and 59.2 mm on Days 10, 20, 30, 40 and 50, respectively, after ovulation. The vesicle remained spherical up to Day 17.8 ± 0.4 but thereafter became irregular in outline. The embryo was first detected on Day 19.9 ± 0.2 and heart beats were noted on Day 21.8 ± 0.3. The mean values for width x crown‐rump length of the embryo/foetus were 3 times 4, 8 times 12, 11 times 17, 13 times 32 and 19 times 47 mm on Days 20, 30, 40, 50 and 60, respectively. The allantoic sac was first detected between Days 19 and 23 and it occupied approximately 25, 50 and 75% of the embryonic vesicle on Days 30, 33 and 38 respectively. The embryo was situated in the dorsal pole of the vesicle by Day 34.8 ± 0.7 and an umbilical cord was first observed on Day 41.1 ± 0.8, coincident with descent of the foetus.

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Investigating factors that could affect milk production of cows is an important way to improve the efficiency of production systems. The purpose of this study was to verify and quantify the influence of calf sex on milk production and lactation length in herds of Holstein, Gir, and Guzera cows. Data from 10,780 lactations of 4,807 Holstein cows that calved between 2001 and 2013; 18,898 lactations of 13,172 Gir cows that calved between 1985 and 2013; and 5,277 lactations of 3,972 Guzera cows that calved between 1987 and 2013 were used. Both the accumulated 305-day milk yield (P305) and the length of the lactation period up to 305 days (DL305) were evaluated. Analysis of variance was performed by the least squares method using the GLM procedure in the SAS statistical program. The P305 was not influenced by the sex of the calf in the Holstein breed. However in the zebu breeds (Gir and Guzera), both P305 and DL305 were significantly affected (P < 0.01) by the sex of the calf, with higher production and average length of lactation in cows that calved males. In addition, a significant difference was also nested within sex of calf and age at first calving (P < 0.05) in the Gir breed. The results indicate that for the zebu breeds, calf sex influences production characteristics. Key words: Milk production. Lactation. Lactation length. ResumoA investigação de fatores que interferem na produção de vacas leiteiras é de grande importância para eficiência dos sistemas de produção. O objetivo do trabalho foi verificar e quantificar a influência do sexo do bezerro sobre produção de leite e sobre a duração da lactação em rebanhos das raças Holandesa, Gir Leiteiro e Guzerá. ocorridas entre 1987 e 2013, de 3.972 vacas Guzerá. As características estudadas foram produção de leite acumulada em 305 dias e duração da lactação (até 305 dias). A análise de variância foi realizada pelo método de quadrados mínimos, através do procedimento GLM do programa estatístico SAS. A produção de leite acumulada aos 305 dias (P305) na raça Holandesa não foi influenciada pelo sexo do bezerro. Entretanto, para os animais de origem zebuína (Gir leiteiro e Guzerá), ambas as características foram significativamente influenciadas (P<0,01) pelo sexo do bezerro, sendo observadas maiores produções de leite e duração de lactação para vacas que pariram machos. Também foi observada diferença significativa do sexo do bezerro aninhado dentro de idade da vaca ao parto (P<0,05) para a raça Gir leiteiro. Estes resultados indicam que para as raças zebuínas, o sexo do bezerro influenciou as características de produção. Palavras-chave: Produção de leite. Lactação. Duração da lactação.

This study aimed  to evaluate the effect of lactation on first follicular wave surge of crossbred (Gir x Holstein) dairy cattle.  Nine multiparous crossbred dairy cattle were divided according to daily milk production (Group 1 = milk production higher than average, n = 5; Group 2 = milk  production  lower  than  average,  n  =  4).  From  calving  (Day  0)  until  divergence  of  first follicular wave, ovaries  was monitored daily by ultrasound exams to observed the follicular emergence,  growth  rate,  maximum  follicular  diameter,  day  of  follicular  divergence  and ovulation. The mean of milk production was 17.4 + 6.4 L/day (n= 9). Group 1 had higher daily milk production than Group 2 (21.8 + 3.8 L/day vs. 11.9 + 3.9 L/day, P< 0.001). Data of follicular emergence were similar in both groups (P >0.05). The growth  rate of first follicular surge was higher  in  Group  2  than  Group  1  (2.0  + 0.0  mm/day  vs  1.2  + 0.6  mm/day,  P<  0.05).  The maximum follicular diameter was 11.6  + 0.9 mm (Group 1) and 13.5  + 1.7 mm (Group 2); P< 0.05. The follicular divergence occurred earlier  in Group 1 than Group 2 (12.2  + 0.8 days vs 13.7 + 0.6 days; P< 0.05). One animal of Group 2 ovulated. In conclusion, data suggested that milk production had influence on ovarian follicular dynamic after calving.Keywords: Follicle, post-partum, lactation, dairy cattle