Ovarian follicle populations, steroidogenicity and micromorphology at 5 and 9 weeks post partum in beef cows in two levels of body condition

Abstract

The effect of body condition at calving on ovarian follicle characteristics during post-partum anoestrus was studied in 38 suckling Blue-Grey cows with mean body-condition scores of 2-80 (s.e. 0-05) (H) or 2-35 (s.e. 0-05) (L) at calving and fed so that they maintained live weight and body condition during lactation. Cows of each level of body condition were ovariectomized at either 5 or 9 weeks after calving and follicles ^3 mm in diameter were dissected out and incubated in a medium (Medium 199) for 2 h. Follicle incubates were assayed for progesterone, testosterone and oestradiol. L cows had fewer follicleŝ 3 mm in diameter than H cows (24-1 v. 44-9; P < 0-05) at 5 weeks post partum due to a lower number of small (3 to 4 mm) follicles (12-9 v. 30-6; P < 0-05). At 9 weeks there was no effect of body condition on mean numbers of follicles (38-1 v. 40-4; P > 0-05). The proportions of healthy, intermediate and atretic follicles in all cows were 0-35, 0-20 and 0-45 respectively; these proportions were not affected by body condition or time of ovariectomy. Body condition did not affect the overall mean capacity of the cultured follicles to produce oestradiol or progesterone in vitro but testosterone production was higher in follicles from H than L cows (6406 v. 5206 pg/h; P < 0-05). However, at 9 weeks post partum a greater proportion of H than L cows had a large (>8 mm), healthy, highly oestrogenic follicle (4/8 v. 1/7; P = 0-18).At 9 weeks post partum, the four large, healthy, oestrogen-active follicles (those secreting >250 pg/h) from H cows were approximately 11-fold more oestrogenic than the single comparable follicle from L cows (7100 v. 635 pg/h; P > 0-05). There was little difference at week 5 post partum: 3288 and 2785 pg/h (P > 0-05) for H and L cows respectively. Oestrogen-active follicles from H cows were significantly more oestrogenic at 9 than 5 weeks post partum (5807 v. 3021 pg/h; P < 0-05). The results suggest that the body condition-related reduction in the number and steroidogenic capacity of large oestrogenic follicles in post-partum cows may be associated with a reduction in LH pulsatility.

Follicle populations, ovulation rates and profiles of gonadotropins, inhibin and insulin-like growth factor-1 of heifers actively immunized against androstenedione and inhibin, separately or in combination

“…The follicular fluid concentrations and patterns of oestradiol, progesterone, and testosterone secretion by oestrogenic and non-oestrogenic follicle in the present study are similar to those reported previously (Spicer, Matton, Echternkamp, Convey and Tucker, 1987;Prado et al, 1990). The absence of any treatment effects on the patterns of follicle steroid content and secretion rate indicates that although the incidence of oestrogenic/dominant follicles (potentially ovulatory follicles) is affected by these immunization procedures, the degree of steroidogenicity of follicles within each class (oestrogenic or non-oestrogenic) was not affected.…”

“…All follicles which produced more than 250 pg oestradiol per h were classified as oestrogenic, an arbitrary definition used previously by Prado, Rhind, Wright, Russel, McMillen, Smith and McNeilly (1990). Some animals had more than one oestrogenic follicle.…”

Induced ovulation of the first postpartum dominant follicle in beef suckler cows using a GnRH analogue

“…In addition, the proportion of beef cows in low body condition at 9 weeks post partum with large oestrogenic follicles was significantly decreased compared with controls (Prado et al, 1990). The oestrogen content of follicles classed as oestrogen active in beef heifers that were rapidly losing weight was sig¬ nificantly decreased compared with the oestrogen content of similar follicles in heifers gaining weight , suggesting that nutritionally induced changes in gonado¬ trophins also affect the physiological function of dominant follicles.…”

Caracterização de pastagem nativa com predominância de Eragrostis plana Nees e desempenho reprodutivo de vacas primíparas suplementadas

“…Conforme Osoro (1986) para obter bons níveis de concepção é necessário que as vacas entrem na época de reprodução, principalmente vacas em lactação, em bom estado corporal, que deve ser mantido durante este período. A importância da condição corporal se reflete na atividade dos ovários das vacas uma vez que animais em melhores condições corporais possuem maior número de folículos nos ovários e maior incidência de folículos com capacidade de ovular (Prado et al, 1990). Richards et al (1986) observaram vacas perdendo condição corporal durante o período de acasalamento, com condição corporal abaixo de 2,5 (escala de 1 a 5) resultando em bloqueio da atividade cíclica reprodutiva, a qual só foi reiniciado quando as mesmas atingiram condição corporal 2,8, ao contrário daquelas que mantiveram ou aumentaram sua condição corporal.…”