Effects of environmental factors on milk yield, lactation length and dry period in Tunisian Holstein cows
- M hamdi, N. Mahdi, B. Frouja, S. Ressaissi, Y. Brar, M. B. Hamouda
The aim of this study was to investigate the interactive and main effects of parity numbers, parity seasonand parity month on postpartum fertility parameters [ovarian rebound (OR), days open (DO) and number of services per conception (S/C)] in Holstein dairy cows. Overall, 418 Holstein dairy cows [winter (December: 9, January: 13, and February: 15) spring (March: 14, April: 34, and May: 36), summer (June: 59, July: 76, and August: 50), and fall (September: 44, October: 47, and November: 21)] were used in this study. The main effect of season showed a significant (P<0.0001) decrease of days from parturition until OR in spring (20.69 ± 4.98) than other seasons [winter: 30.97 ± 16.18, summer: 23.71 ± 6.31and fall: 21.93 ± 4.63]. Also, Do was found to be decreased in fall (99.18 ± 42.75, P<0.0001) than other seasons [winter: 189.5 ± 107.75, summer: 156.87 ± 56.05 and spring: 219.20 ± 55.06]. Moreover, the main effect of parturition month was also significant (P<0.0001) on both OR and DO. The days from parturition to OR were decreased in March (20.36 ±8.1) and April (20.52 ± 4.56) than other months of the year. Meanwhile, the DO was decreased in November (86.33 ±41.57, P<0.0001). Further, the parity number affected significantly DO (P<0.0001) but not OR (P=0.804). The days open was longer (177.65 ± 69.22) afterfirst parturitionand shorter (95.66 ± 35.97) after the 6 th one than other parity numbers.The interaction effects of parity season, months and number on postpartum fertility parameters were alsosignificant (P < 0.0001).Ovarian reboundwas decreased after1 st , 3rd and 4 th parturition inspring, fall and summer mainly in March, October and August (16.50±3.21, 16.33±4.04 and 14±1.41, respectively).Whereas, DO was decreased after1 st parturition in autumn mainly in November (66.83±26.46). Non significant relation (P=0.6) was estimated between parity number and S/C. However, the season has a significant effect (P<0.02). We concluded that, the parity numbers, season and month have a significant effects on postpartum fertility parameters.