Abstract

DOMINGUEZ, Carlos E.; GARMENDIA, Julio  and  MARTINEZ, Nelson. Influence of Calving Season, Body Condition and Supplementation on Postpartum Ovarian Activity of Crossbred Cows under Mixed Pasture Grazing in Northern Guárico State, Venezuela. Rev. Fac. Cienc. Vet. [online]. 2007, vol.48, n.1, pp.37-50. ISSN 0258-6576.

The aim of this estudy was to evaluate the influence of either calving season, body condition score and supplementation on changes of the ovarian activity before 90 days post calving. Sixty crossbred cows were subjected to a completely randomized design, grazing native forages (Panicum maximun and Cynodon sp.), and asigned to two treatments (T1: grazing + supplementation during 45 days pre calving and 90 days post calving and T2: grazing + supplementation during 90 days post calving). Progesterone levels in skimmed milk and ovarian activity were recorded twice a week. Samples of forage and supplement were analyzed by season. Supplement intake was registered weekly. Variables studied were: Treatment (T1 and T2); Season of Calving (SC): 1 (April-May), 2 (June-September), and 3 (October-January); Girth Height (GH); Body Condition Score (BCS): poor (2), moderate (≥2.5) and good (>3) and number of follicles by class: I (≤ 5mm); II (6-9 mm) and III (≥10mm). GH was used as covariate. Data were analyzed using an additive linear model by least square methodology (SPSS 7.5). Class IIIfollicles were analyzed using Kruskal-Wallis test. Both, frecuency of corpora lutea and luteal activity were analyzed by contingency tables and compared with Chi-square χ². Treatments did not affect either the onset of luteal activity (p>0.05) luteal activity frequency. Class I and III follicles were not affected (p>0.1) by treatment, but class II follicles were. SC significantly affected class I and class III follicles (p<0.001). Cows with BC>3 showed a higher number of class I, II, III follicles than cows with BC=2 and this effect was significant (p<0.001). Treatment 1 during both, dry and transitional season, apparently promoted growth of small follicles (≤5 mm). Corpora lutea were not affected by treatment but SC affected (p<0.01) corpora lutea number, being 71.4 % of them detected during the transitional season. These results suggest a seasonal effect on follicular population, and corpora lutea influenced by body condition, on reproductive performance.

Keywords : Cows; livestock; multipurpose breeds; body condition; seasons; parturition; supplements; Guárico.

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