TAI increases reproductive efficiency in intensive pasture based milk production systems

The aim of this study was to evaluate the reproductive efficiency of dairy cows kept on pasture feeding system with corn silage and 16% crude protein concentrated supplementation, submitted to three different reproductive programs. The experiment took place in three small farms, with two Jersey herd and average milk production of 21 liters a day and another herd of Holstein and Simmental crossbred cows with average milk production of 28 liters a day. The farms regularly used estrus detection and Artificial Insemination (AI), performed twice a day, when the animals were brought to the milking and feed. Multiparous cows were selected by reproductive history and subjected to complete gynecological evaluation between 30-40 days postpartum. All females considered healthy were randomly allocated to one of three treatments: control - Cows (n = 58) were inseminated 12 hours after the start of the first natural estrus occurred, after 50 days in milk. In PGF treatment, each cow (n = 43) with 50-60 days postpartum received an IM dose of 0.5 mg of d-cloprostenol and was inseminated 12 hours after detection of estrus. Cows not entering into heat received a second dose of 0.5 mg d-cloprostenol between 11 to 14 days later. In the Fixed Time Artificial Insemination (FTAI) treatment, cows (n = 47) were inseminated at fixed time. The protocol was initiated 50-60 days postpartum with 1g progesterone intravaginal device and IM administration of 2.0 mg of estradiol benzoate (EB; D0). In D8, the device was removed and administered 0.5 mg of D-cloprostenol and 1 mg estradiol cypionate (IM). The FTAI was performed 48 hours after implant removal. Pregnancies diagnosis occurred 30 days after AI with ultrasound assistance. Empty cows returned to conventional management of the property and the IA until the 150 days in lactation (DIM) were recorded and later examined by US. The DIM for the first IA (DIM/IA) and calving conception interval (CCI) variables were examined by analysis of variance followed by Tukey's test. Deviance analysis was applied to the conception rates to first insemination (CR); and pregnancy at 150 days in milk (P150). A significance level of 5% was set for all statistical tests employed in this study. The effects of farm, parturition order, ovarian condition, body condition score, breed and dairy production had no significant interaction with experimental treatments. As expected, there was a reduction in DIM/IA for FTAI (65.49 ± 0.64 days)b and PGF treatments (68.07 ± 1.76 days)b, compared to the control (77.59 ± 3.01 days)a. The conception rate was higher in the IATF (78.72 ± 6.03%)a in relation to PGF (53.49 ± 7.70%)b and the control (51.72 ± 6.62%)b. The pregnancy rate at 150 DIM (P150) was higher than the use of FTAI (90.01 ± 4.38%)a compared to the control group (70.59 ± 6.44%)b and PGF group (67.50 ± 7.50%)b. The CCI of pregnant animals at 150 DIM was reduced by FTAI treatment (68.55 ± 2.17 days)a, when compared to control groups (89.31 ± 4.80 days)b, and PGF (73.33 ± 4.30 days)b. The better results obtained in FTAI possibly were due to a positive effect of hormonal protocol combined with high service rate. It was conclude that, at the observed experimental conditions, FTAI improved reproductive efficiency of dairy herds exploited at intensive pasture based system.