Comparison of two oestrus synchronisation protocols administered to dairy cows during routine reproduction services

Progesterone-based oestrus synchronisation protocols are frequently used for treatment of cows presented for examination during routine reproduction management service. This study aimed to evaluate the effect of the addition of gonadotrophin-releasing hormone (GnRH) at the start of a progesterone-based oestrus synchronisation protocol for cows presented for examination during routine veterinary service on a commercial dairy farm over 10 months. Overall 139 animals were retained in the study, of which 78 received a standard progesterone-based treatment (STD) and 61 received the same treatment but with the addition of GnRH on day 0 (STD+). Cows were submitted for artificial insemination following observation of behavioural oestrus. Cow and service specific data were used to create two mixed effects generalised linear models to analyse the effect of treatment group on submission rate (SR) and conception rate (CR). In the final SR model lameness had a significant negative association (p=0.01) and STD+ had a non-significant positive association (p=0.12) with submission. In the final CR model only presence of a new CL at day 7 had a significant positive association (p=0.04) while previous reproductive disease had a non-significant positive association (p=0.83) with conception. These results highlight the difficulties in assessing the real effects of altering reproductive protocols on individual farms when other important explanatory variables are considered

Acute dietary restriction in heifers alters expression of genes regulating exposure and response to gonadotrophins and IGF in dominant follicles

Dietary restriction in growing cattle and severe negative energy balance in lactating cows have been associated with altered gonadotropin secretion, reduced follicle diameter, reduced circulating oestradiol concentrations and anovulation. Therefore, we hypothesised that acute dietary restriction would influence the fate and function of the dominant follicle by altering the expression for genes regulating gonadotrophin and IGF response in ovarian follicles. Newly selected dominant follicles were collected 7–8 days after prostaglandin F2α (PGF) administration from heifers (n = 25) that were individually fed a diet supplying 1.2 maintenance (M; control, n = 8) or 0.4 M (restricted, n = 17) for a total duration of 18–19 days. Heifers within 0.4 M were ovulatory (n = 11) or anovulatory (n = 6) depending on whether the dominant follicle present at PGF ovulated or became atretic following luteolysis. Control animals were all ovulatory. Acute dietary restriction decreased IGF-I (P < 0.001) and insulin (P < 0.05) in circulation; oestradiol (P < 0.01) and IGF-I (P < 0.01) in follicular fluid; and mRNA for FSHR (P < 0.01) in granulosa cells but increased mRNA for IGFBP2 (P < 0.05) in theca cells of the newly selected dominant follicle. However, this only led to anovulation when dietary restriction also decreased mRNA for CYP19A1 (P < 0.05), IGF2 (P < 0.01) and IGF1R (P < 0.05) in granulosa cells and LHCGR (P < 0.05) in theca cells of follicles collected from heifers fed 0.4 M. These results suggest that the catabolic environment induced by dietary restriction may ultimately cause anovulation by reducing oestradiol synthesis, FSH-responsiveness and IGF signaling in granulosa, and LH-responsiveness in theca cells of dominant follicles