Anti-Mullerian Hormone (AMH), antral follicle count (AFC), external morphometrics and fertility in Tabapua cows

The intense selection of characteristics related to animal performance may affect the reproductive efficiency of beef cows negatively. Selection for fertility along with production traits is, therefore, readily justifiable. The objective of the present study was to evaluate possible relationships among AFC, serum AMH concentrations and external morphometrics with reproductive efficiency in Tabapua (a Brazilian Bos indicus beef breed) females. Antral follicle counts and external morphometrics were measured in nulliparous (n = 162), primiparous (n = 80) and multiparous (n = 351) cows, from four farms. Age at first parturition (AFP), parturition interval (PI), maternal ability (MA), precocity, rusticity and survival (PRS) and overall reproductive efficiency (BE) were evaluated according to the Brazilian Association of Zebu Breeders (ABCZ) data bank indexes. A single blood sample per animal was collected at random stages of the reproductive cycle from a subset of animals (nulliparous = 84, primiparous and multiparous = 136) to determine serum AMH concentrations. The AFC classes were defined as lesser (< 28), intermediate (28-50) and greater (> 50). Correlations between all variables and the effects of parity and AFC on reproductive traits, AMH and external genitalia size were analyzed by the PROCORR and by the PROCGENMOD procedures of SAS (R) (SAS, Cary, NC, USA), respectively. Antral follicle count did not differ (P = 0.71) among nulliparous (38.6 +/- 23.96) primiparous (47.54 +/- 26.16) and multiparous (41.08 +/- 25) cows and was negatively correlated with pregnancy interval (PI), such that, as PI decreased (r = -0.28; P < 0.005), AFC increased. Vulva width was not affected (P = 0.08) by parity and was larger (P < 0.05) for females in the greater AFC class (8.81 +/- 0.12 cm) compared with the intermediate (8.42 +/- 0.11 cm) and lesser (8.38 +/- 0.13 cm) classes. As vulva width increased, parturition interval decreased (r = -0.15; P < 0.005) and overall reproductive efficiency increased (r = 0.17, p < 0.005). Thoracic depth was associated with greater AFCs (r = 0.10; P < 0.001). Anti-Mullerian hormone concentrations were greater (P < 0.05) for animals in the greater AFC class (1.15 +/- 0.09 ng/mL) compared with the lesser (0.44 +/- 0.02 ng/mL) and intermediate (0.73 +/- 0.05 ng/mL) classes. Vulva width, AFC, external morphometrics and AMH concentrations were moderately associated, considering the low heritability of fertility traits, and should be studied further to be considered in the selection for fertility in Bos indicus cattle.