368 CONCEPTION RATE AT FIRST ARTIFICIAL INSEMINATION WITH SEXED SEMEN OR CONVENTIONAL SEMEN IN CROSSBRED DAIRY COWS

Abstract

The use of sexed semen in dairy cattle almost eliminates the birth of unwanted male calves and can lead to increased milk production by means of genetic selection exerted on the females. However, AI with sexed semen still presents several obstacles to overcome. Holstein-Zebu cows are responsible for 80% of the milk produced in Brazil. These crossbred animals are used extensively throughout the country because their physiologic and morphologic characteristics are compatible with milk production in the tropics which results in an economic performance advantage. The objective of this study is to evaluate the conception rates with sexed semen, comparing it to the use of non-sorted semen in crossbred dairy cows. In addition, two insemination times had been studied to determine the best timing for AI with the sexed semen. Both studies were carried out in the Experimental Station Seropedica of Pesagro-RJ, located in the state of Rio de Janeiro, Brazil. The experiment was done in 2008/2009 (January to April). In the first Trial 56 Holstein-Zebu females, composed of 1/2 to 7/8 Holstein genetics, were inseminated 12 h after estrus detection with non-sorted semen (control group n = 29, 14 heifers and 15 cows) or with sexed semen (experimental group n = 27, 13 heifers and 14 cows). The semen utilized was from the same bull and thawing was performed intravaginally. In the second trial, 55 females were inseminated only with sexed semen from the same bull, with thawing in water at 35°C, at two different times: 12 h after estrus observation (control group n = 27, 12 heifers, 4 primiparous, and 11 multiparous) and 15 h after estrus observation (experimental group n = 28, 12 heifers, 5 primiparous, and 11 multiparous). The pregnancy diagnoses were done by rectal palpation and transrectal CAT scan at Day 45. Statistical analyses had been done using Chi-square. The conception rate in the first trial was of 17.2% (5/29) for sexed semen and 53.8% (14/26) for non-sorted semen (P < 0.05). In the second trial, the conception rate was of 37.0% (10/27) for insemination with sexed semen, 12 h after estrus observation and 50.0% (14/28) for the females inseminated 15 h after estrus observation (P > 0.05). It is possible that one of the causes of fertility reduction with sexed semen is that sexed-sperm remain viable for a shorter time after the insemination. Inseminations with sexed semen done 15 h after estrus detection, which can be more synchronized with the time of ovulation, and when accompanied by closely controlling the thawing process, show results similar to those obtained with conventional semen.