Managing the dominant follicle in lactating dairy cows

Reproductive efficiency is not optimal in high-producing dairy cows. Although many aspects of ovarian follicular growth in cows are similar to those observed in heifers, there are numerous specific differences in follicular development that may be linked with changes in reproductive physiology in high-producing lactating dairy cows. These include: I) reduced circulating estradiol (E2) concentrations near estrus, 2) ovulation of follicles that are larger than the optimal size, 3) increased double ovulation and twinning, and 4) increased incidence of anovulation with a distinctive pattern of follicle growth in anovular dairy cows. The first three changes become more dramatic as milk production increases, although anovulation has not generally been associated with level of milk production. To overcome reproductive inefficiencies in dairy cows, reproductive management programs have been developed to synchronize ovulation and enable the use of timed AI in lactating dairy cows. Effective regulation of the CL, follicles, and hormonal environment during each part of the protocol is critical for optimizing these programs. This review discusses the distinct aspects of follicular development in lactating dairy cows and the methodologies that have been utilized in the past two decades in order to manage the dominant follicle during synchronization of ovulation and timed AI programs. (C) 2011 Published by Elsevier B.V.

Ovarian response of Suffolk ewes to estrous synchronization using short-term protocol

The efficacy of estrus synchronization using short-term protocol was evaluated by ultrasound exams in Suffolk ewes during the pre-breeding season. The control Group (n = 12) was synchronized by treatment for 12 days with vaginal sponges impregnated with medroxyprogesterone acetate, and 400 IU eCG at sponge withdrawal. Experimental groups I, II and III kept the sponge in place for 4 days, and 100 µg of PGF2a was administered at sponge withdrawal. Additionally, Group I (n = 12) had 0.1 mg of estradiol benzoate (EB) administered during sponge placement and 50 µg of GnRH 48 hours after sponge removal. Group II (n = 6) had 35 mg of progesterone (P4) injected, and 0.1 mg of EB administered during sponge placement, 400 IU eCG at withdrawal and 48 hours after, 50 µg GnRH were administrated. Group III (n = 12) had 35 mg of P4 and 0.2 mg of EB administered at sponge placement, 400 IU eCG at withdrawal, and 50 µg of GnRH was administrated after 56 hours. Ovaries were monitored through ultrasound scanning. Concerning the first wave, no difference was detected between the control group and the experimental groups. However, the characteristics of ovulatory wave were significantly different between the groups. The duration of the follicular wave was shorter for Group III than for Group II. The follicle in Group I reached its maximum diameter before the Group II. The diameter of the follicle at the sponge withdrawal in the control group was larger than in Group I. After sponge withdrawal, the follicular growth rate was smaller in the control group than in Group III. The maximum diameter of the follicle in Group II was larger than in the other groups. The short-term protocol in which estrogen was used did not synchronize the emergence of the wave of follicular development.

Factors affecting fertilisation and early embryo quality in single- and superovulated dairy cattle

Data on fertilisation and embryo quality in dairy cattle are presented and the main factors responsible for the low fertility of single-ovulating lactating cows and embryo yield in superovulated dairy cattle are highlighted. During the past 50 years, the fertility in high-producing lactating dairy cattle has decreased as milk production increased. Recent data show conception rates to first service to be approximately 32% in lactating cows, whereas in heifers it has remained above 50%. Fertilisation does not seem to be the principal factor responsible for the low fertility in single-ovulating cows, because it has remained above 80%. Conversely, early embryonic development is impaired in high-producing dairy cows, as observed by most embryonic losses occurring during the first week after fertilisation. However, in superovulated dairy cattle, although fertilisation failure is more pronounced, averaging approximately 45%, the percentage of fertilised embryos viable at 1 week is quite high (>70%). Among the multifactorial causes of low fertility in lactating dairy cows, high feed intake associated with low concentrations of circulating steroids may contribute substantially to reduced embryo quality. Fertilisation failure in superovulated cattle may be a consequence of inappropriate gamete transport due to hormonal imbalances.

Neospora caninum infection dynamics in dairy cattle

Neospora caninum is considered in many countries as one of the key abortion agents in cattle. This study aims to investigate the parasite behavior in dairy cattle in the municipality of Avar,, SP, Brazil, where abortions frequently occur. An ELISA was performed to compare two samplings on a total of 615 animals; tests were performed in the same herds with a gap of 3 years. An increase in the percentage of reactive animals was observed, ranging from 21.6% at the first sampling to 38.9% at the second sampling. of the 176 animals tested at both samplings, 61.93% retained a non-reactive status, 15.9% retained a reactive status, 19.88% switched from non-reactive to reactive and 2.27% switched from reactive to non-reactive. of the 100 animals with reproductive disturbances, 50% presented anti-Neospora antibodies, thereby indicating the presence of the protozoa. When comparing cows and their respective female offspring, a predominance of horizontal infection was observed. Moreover, considering the significant percentage of animals that switched from non-reactive to reactive and the abundant presence of dogs among the herds, the N. caninum transmission may be attributed to presence of carnivores.

Follicular Development in Ewes During Natural and Prostaglandins Induced Estrous Cycle

The follicular development was evaluated in ovine females during natural and prostaglandin-F(2 alpha) (PG) induced estrous cycle. Ewes were randomly divided in two treatments (n=7/treatment): T1 with natural cycle and T2 synchronized with two injections of PG. From one day before PG injection until next ovulation, daily transrectal ultrasonography was done. All follicles >= 2 mm were assessed. During the interovulatory intervals, follicular growth and regression occurred in a wave like pattern (2-3 waves). The maximum diameter of the largest follicle of the first wave was greater in T1 (5.83 +/- 0.31 mm) compared with T2 (5.0 +/- 0.1 mm; P<0.01), but there was no significant difference among the emergency day of largest follicle, during the growth phase of the follicular waves. The duration of the plateau phase in wave 2 differed between the two treatments (P<0.05) showing 0.83 +/- 0.31 and 1.83 +/- 0.17 d, for natural and synchronized treatment, respectively. Growth rate did not differ between treatments. Presence of new luteal tissue was detected on day 3 after ovulation. In conclusion, the follicular development was similar in female ovine during natural and PG induced estrous cycle.