Produção de leite, leite residual e concentração hormonal de vacas Gir × Holandesa e Holandesa em ordenha mecanizada exclusiva

In a machine milking system in which calves were not present, oxytocin concentration (OT), cortisol release (CORT), milk yield and residual milk were evaluated for cows of three genetic groups: 1/2Gir x 1/2Holstein (n=6, genetic group F2), 1/4Gir x 3/4Holstein (n=6, genetic group F3) and Holstein (n=6, genetic group H). Group H had higher milk yield than groups F2 and F3, whereas OT was similar among groups. The increase in OT during milk-ing was greater for H and F3 than for F2. Residual milk for F2 was' higher than for F3 and H. The CORT for F2 was higher than for cows of the other two genetic groups. Cows from F2 and F3 were more stressed than H cows during machine milking, but the Gir x Holstein groups did release suffficient OT to induce an effective milk letdown response.

Staphylococcus aureus: Resistance patterns to antimicrobials and Penicillinase among strains isolated from apparently healthy lactating cows

Ninety-two strains of Staphylococcus aureus isolated from the nasal fossa and udder skin of apparently healthy lactating cows were analyzed for resistance to antibiotics and production of penicillinase.The results showed a greater frequency of resistance patterns to penicillin and ampicillin.All strains were sensitive to oxacyllin and gentamicin.The most frequent Barber and Burston model was SSSS (60.90%), followed by RSSS (18.50%).With respect to the production of penicillinase although the Lucas method indicated a larger number of positive samples, we suggest the use of the Haight and Finland method due to a greater consistency of data obtained with it.

Synchronization rate, size of the ovulatory follicle, and pregnancy rate after synchronization of ovulation beginning on different days of the estrous cycle in lactating dairy cows

Recently a protocol was developed that precisely synchronizes the time of ovulation in lactating dairy cows (Ovsynch; GnRH-7d-PGF(2 alpha)-2d-GnRH). We evaluated whether initiation of Ovsynch on different days of the estrous cycle altered the effectiveness of this protocol. The percentage of cows (n=156) ovulating to the first GnRH was 64% and varied (P<0.01) by stage of estrous cycle. Treatment with PGF(2 alpha) was effective, with 93% of cows having low progesterone at second GnRH. The overall percentage of cows that ovulated after second GnRH (synchronization rate) was 87% and varied by response to first GnRH (92% if ovulation to first GnRH vs 79% if no ovulation; P<0.05). There were 6% of cows that ovulated before the second injection of GnRH and 7% with no detectable ovulation by 48 h after second GnRH. Maximal diameter of the ovulatory follicle varied by stage of estrous cycle, with cows in which Ovsynch was initiated at midcycle having the smallest follicles. In addition, milk production and serum progesterone concentration on the day of PGF(2 alpha) affected (P<0.05) size of the ovulatory follicle. Using these results we analyzed pregnancy rate at Days 28 and 98 after Al for cows (n=404) in which Ovsynch was initiated on known days of the estrous cycle. Pregnancy rate was lower for cows expected to ovulate larger follicles than those expected to ovulate smaller follicles (P<0.05; 32 vs 42%). Thus, although overall synchronization rate with Ovsynch was above, 85%, there were clear differences in response according to day of protocol initiation. Cows in which Ovsynch was initiated near midcycle had smaller ovulatory follicles and greater pregnancy rates. (C) 1999 by Elsevier B.V.

Heritability estimate for stayability in nelore cows

The objective of the present study was to determine the possibility of using stayability (STAY) of dams as a selection criterion for fertility in the Nelore breed. STAY was defined as whether or not a cow calved in a herd at a specific age or after this age given that she had calved at an earlier age. The specific ages studied were 5 (STAY5), 6 (STAY6) and 7 (STAY7) years. Data on 53 271, 46 011 and 41517 animals were analyzed for the respective ages. The Method 91 was used to estimate the variance components and a maximum threshold a posteriori model was used to predict the genetic values. The analyses provided h(2) estimates of 0.117+/-0.003, 0.122+/-0.004 and 0.171+/-0.005 for STAY5, STAY6 and STAY7, respectively. The ease with which the trait can be recorded and the h 2 estimates indicate that the use of this trait as a selection criterion can contribute to increased dam fertility. (C) 2002 Elsevier B.V. B.V. All rights reserved.