| چکیده انگلیسی مقاله |
The transition period in dairy cows at the end of the lactation period and the first weeks of milk production at the beginning of the next lactation period are the foundation for the success or failure of the entire lactation period. The entire dry period is important in terms of preparing the cow for the next lactation period, but the final three weeks of the dry period (the pre-calving transition period) and the following three weeks of lactation (the post-calving transition period) are particularly important in this regard. The beneficial effects of omega-3 nutrition have been shown in previous studies, such that dietary supplementation of fatty acids affects the concentrations of prostaglandins, steroid hormones, and growth factors. As a result, increased follicular growth and luteal activity can improve fertility in dairy cows. Tryptophan, as an essential amino acid, affects feed intake, growth performance, reproduction, neural function, immunity, and anti-stress responses in monogastric animals and ruminants. Therefore, the aim of the present study was to investigate the effect of omega-3 and N-acetyl tryptophan feeding on ovarian cycle resumption and follicular dynamics in Holstein dairy cows during the transition period.
Material and Methods: One hundred and twenty pregnant Holstein cows with multiple calvings were selected based on expected calving and randomly assigned to treatments. Cows with a history of mammary, locomotor, or other diseases during the current calving were excluded. Also Cows that were outside the normal range in terms of body condition score (BCS greater than 4 and less than 3) were excluded from the list. In such a way that cows in each experimental group had the same conditions in terms of calving time (1.3 ± 1.2) and body condition score (2.3 ± 0.2). Cows were assigned to one of four treatment groups from day 30 before calving to day 80 after calving based on a 2x2 factorial design: 1- cows fed a diet without coated tryptophan and saturated fatty acids (SFA), 2- cows fed a diet without coated tryptophan and omega-3 fatty acids, 3- cows fed a diet with coated tryptophan and no saturated fatty acids (SFA), and 4- Cows fed a diet with coated tryptophan and omega-3. Plasma concentrations of progesterone (days 14, 24, and 34 after parturition) and estradiol 17 beta (day of ovulation) were measured using an ELISA reader (STAT FAX 2100). For this purpose, Diaplus ELISA kits manufactured in Canada with kit numbers 4810185 and 49101123 were used. All animals were ultrasound scanned weekly from day 14 postpartum to day 60 postpartum to assess follicular dynamics (dominant follicle diameter, corpus luteum diameter, and ovulation). A change in the color and shape of a pre-identified large follicle was considered as ovulation of the dominant follicle. One or two large follicles together with a number of small follicles were considered as a follicular wave. Cows with progesterone concentrations greater than 1 ng/ml in at least two consecutive blood samples were considered to have luteal activity (Stevenson, 1997). Final data analysis was performed using the GLM procedure, using SAS statistical software version 9.1 (SAS, 2001). Comparison of treatment means was also performed using Duncan's multiple range tests at the 0.05 level of error.
Results: The results showed that the resumption of the ovarian cycle (days) was affected by the interaction effect of omega-3 and tryptophan and was significantly earlier in cows fed omega-3 and tryptophan than in other groups (P<0.05). The interval from calving to the first ovulation (days) after calving was affected by the interaction effect of omega-3 and tryptophan and was significantly shorter in cows fed omega-3 and tryptophan than in other groups (P<0.05). Ovulatory follicle diameter (mm) and corpus luteum diameter (mm) were affected by the interaction of omega-3 and tryptophan and were significantly larger in cows fed omega-3 and tryptophan than in other groups (P<0.05). Dominant follicle diameter was affected only by omega-3 feeding (P<0.05), and the effect of tryptophan feeding and the interaction of omega-3 and tryptophan were not significant (P<0.05). Estradiol concentration (picogram/mL) at the time of ovulation was significantly higher in cows that received omega-3 and tryptophan than in other groups (P<0.05). Progesterone concentration (nanogram/mL) after calving was significantly higher in cows that received omega-3 and tryptophan than in other groups (P<0.05).
Conclusion: In general, the results of the present study showed that omega-3 and N-acetyl tryptophan feeding had a positive effect on the resumption of the ovarian cycle and follicular dynamics in Holstein dairy cows during the transition period, and by shortening the interval from calving to the first ovulation, faster resumption of ovarian cycles after calving, and increasing the diameter of the ovulatory follicle and the diameter of the corpus luteum, it had a positive effect on increasing fertility. The results of this study can be used on a larger scale.
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