Abstract
The objective of the study was to evaluate the effects of three nutritional treatments, which differed in energy level and source, on preovulatory follicles, number of follicles and oestrous activity in dairy cows. Twenty two Holstein multiparous cows from the Elsenburg herd were used in this study. After parturition, cows were kept on kikuyu-ryegrass pastures on an ad libitum basis, and allocated to various levels and types of concentrate supplements, which differed in starch and fat contents. The control group received 7 kg/day of a control concentrate, and the treatment groups each received 12.6 kg/day of concentrate. The concentrates contained high starch-low fat (HSLF) and high starch-low fat/low starch-high fat (HSLF-LSHF) levels. The supplement in treatment HSLF was a glucogenic concentrate using maize as the energy source. The supplements in treatment HSLF-LSHF were a combination of a glucogenic concentrate, which was offered for the first 60 days in milk (DIM), similar to treatment HSLF, followed from 61 DIM by a lipogenic concentrate using wheat bran and calcium (Ca) salts of long-chain fatty acids as the energy sources. At 80 ± 10 DIM, cows were synchronized with an Ovsynch protocol without being inseminated before the ultrasonography observation. While they were detained in a shaded neck clamp, cows were assessed individually with an ultrasound scanner every three days for ovarian measurements and follicular activity until the subsequent oestrus. Results showed that ovarian and follicular measurements and the numbers of follicles in various follicle size classes were similar between nutritional treatments. However, the total ovarian follicular counts were significantly higher in cows that received the HSLF and HSLF-LSHF treatments, compared with their counterparts in the control group (i.e. 7.23 ± 0.22, 7.21 ± 0.14 and 6.53 ± 0.19, respectively), through possible improvement in nutritional status. Further research is required to investigate various energy levels and sources that enhance the viability and the quality of the oocyte ovulating from the dominant follicle and improve the intensity and length of the oestrous expression in dairy cows.Keywords: Energy nutrients, follicular numbers, heat expression, preovulatory follicle, ruminant
Highlights
Optimizing fertility in dairy herds requires cows to calve annually to maximize the economic returns from milk production (Roche et al, 2000)
Number of cows Ovarian and follicular dimensions Short diameter of the ovary Long diameter of the ovary Ovarian area Area of preovulatory follicles at first observation Follicular counts Number of small follicles Number of medium follicles Number of large follicles Number of total follicles Proportion of cows ovulating and pregnant3 Proportion of cows ovulating after Ovsynch Proportion of cows showing oestrous expression Pregnancy rate after AI
No differences were observed between nutritional treatments in the dimensions of the ovaries and the preovulatory follicles and numbers of follicles in various classes in dairy cows
Summary
Optimizing fertility in dairy herds requires cows to calve annually to maximize the economic returns from milk production (Roche et al, 2000). Anoestrus is caused by low levels of metabolites (i.e. glucose) and hormones (i.e. insulin, insulin-like growth factor-I (IGF-I), luteinizing hormone (LH) and oestradiol) in the bloodstream (Beam & Butler, 1999; Diskin et al, 2007). The decline in these metabolic and endocrinal signals reduces the diameter and growth rate of the dominant follicle (Beam & Butler, 1997), prevents or delays it from ovulating (Butler, 2003; Webb et al 2004), and eventually decreases the weight of the corpus luteum after ovulation
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