Applying variations of the Ovsynch protocol at the middle of the estrus cycle on reproductive performance of lactating dairy cows during summer and winter.

Two modifications of the Ovsynch protocol, GnRH+TAI after PGF(2 alpha) 48 h (CO-48) or 72 h (CO-72), were compared with the original protocol (OVS: GnRH-7 d-PGF(2 alpha)-2 d-GnRH-16 h-TAI) to study their effects on reproductive performance in 785 lactating dairy cows (Holstein Friesian, Bos Taurus). Results showed that more cows (P<0.001) returned to estrus within a week after TAI with CO-48 treatment compared with that in OVS and CO-72 treatments. Pregnancy rates were greater (P<0.001) for the CO-72 cows than those for both OVS and CO-48 treatments and for primiparous cows compared with multiparous cows. Moreover, pregnancy rates were lower in summer compared with those in winter. Pregnancy losses for cows in both CO-48 and CO-72 were greater (P<0.05) than that for cows in OVS treatment. Pregnancy losses were greater in summer (P<0.001) than in winter and for multiparous cows (P<0.001) than for primiparous cows. In conclusion, primiparous and winter-bred cows had greater pregnancy rates and fewer pregnancy losses than those of multiparous cows and summer-bred cows, respectively. Because of the presence of significant treatment, parity, and season interactions, TAI with ovulation synchronization protocols should be tailored according to the season and parity. CO-72 is recommended for primiparous cows but not for multiparous cows, and CO-48 is not recommended for synchronization. Furthermore, cows that exhibited estrus at any time were inseminated to improve pregnancy rates in ovulation synchronization protocols.

Relationships of productive life evaluations with changes in evaluations for yields.

The objective of this work was to investigate the relationships of productive life with changes in bull evaluations for yield traits. Two datasets were analyzed. In the first, predicted differences for change in milk yield from first to second lactation of daughters of artificial insemination (AI) Holstein bulls used widely in the southeastern United States were available from a previous study. These were correlated with predicted transmitting abilities (PTA) of productive life from May 2000 USDA sire evaluations. Based on bulls with at least 10 daughters (n = 560) the correlation of PTA productive life with predicted differences for the change in milk yield was 0.30. The correlation increased to 0.36 for bulls with at least 50 daughters (n = 319) and to 0.40 for bulls with at least 75 daughters (n = 284). The second analysis included data on 1831 AI sampled Holstein bulls evaluated by USDA between July 1989 and May 2000. Changes in PTA yields were calculated as PTA from evaluations based on first and second records of daughters minus those from first-record evaluations. Correlation analyses showed that PTA yields from first-record evaluation and changes in PTA yields were positively associated with productive life. Regression coefficients on changes in PTA yields were all positive indicating that increases in PTA for yield traits as daughters aged corresponded with longer productive life. Using changes in AI bull evaluations for yields could improve prediction of productive life for little cost.

Variation in fleece characteristics of Awassi sheep at different ages.

Fleece characteristics have economic significance in sheep. When assessing fiber characteristics, the importance of sex, age of sheep and the body location of the sample taken are important considerations. Triplicate fleece samples were obtained from the shoulder, right mid-side and hip of 12 male and 17 female lambs (6-10 months), 62 yearling ewes (14-20 months) and 235 mature ewes (28-84 months) by hand shearing. The greasy fleece weight, staple length, fiber length and fiber diameter measures were 2.1+/-0.03kg, 14+/-0.18cm, 24+/-0.26cm and 36+/-0.33&mgr;m, respectively. Correspondingly, the medullated fibers, inner coat, outer coat and kemp fibers were 11.6+/-0.33, 59.7+/-0.29, 34.0+/-0.23 and 6.3+/-0.16%, respectively. Age had a significant influence on body weight and greasy fleece weight, but male and females were similar. Body location of the sample had a significant effect on the fiber diameter, and percentages of medullated fibers, kemp fibers, and inner coat fibers. The finest fibers and a lower percentage of medullated fibers were found on the shoulder and mid-side, whereas, the percentage of inner coat fibers was highest on the hip. Although there was no significant interaction between body location and age-sex groups for fiber characteristics, it was important for staple and fiber length (P<0.05). The wide variation in fiber diameter and percentage of medullated fibers suggest potential for improvement of economical traits.