PRE-CALVING FIBRE-BASED DIETS FOR DAIRY COWS.

During the transition period, pre-calving cows mobilize their stored body reserves in an attempt to meet the increased demands for pregnancy and growth before calving and milk production after calving. This results because of the immediate post-calving decline in dry matter intake (DMI), which creates a shortage in required nutrients and a state of negative energy balance (NEB). NEB, as evidenced by live weight (LW) loss after calving, is a physiological adaptation that occurs during the immediate post-calving period. To limit the mobilization of reserves, optimal pre-calving dietary management regarding in particular the types and levels of intake of nutrients relative to their requirements are essential, but the effective dietary choices are still inconclusive. Research indicated that feeding high energy levels, which are starch- or fat-based ad libitum is beneficial to transition success. On the down side, overconsumption of energy in pre-calving cows is detrimental to rumen health and liver function and decreases DMI post-calving, thus resulting in poor adaptation to NEB in the subsequent lactation. A possible alternative is to feed fibre-based diets (>400 g/kg of NDF on DM basis) in the pre-calving phase, containing lower digestible energy levels. Research reported in this context showed that such prepartum diets adjusted the DMI to optimise rumen digestion and fermentation, decreased the mobilization of body reserves, and prevented the liver deposition of total lipid and tri-acyl glycerol. Furthermore, feeding fibre-based diets that contained low digestible energy levels to dry cows showed several other benefits, as is evident in fewer health complications, reduced body condition loss, and enhanced reproductive parameters after calving. The hypothesis in the study cited was that by improving the late pre-calving intake of energy and protein per kg on a DM basis to enhance the energy status of the cows can limit the LW loss and improve fertility during the following lactation. The objective of the study, therefore, was to evaluate two late pre-calving fibre-based diets that differed in non-structural carbohydrate (NFC) and protein levels on LW changes and fertility traits of Holstein cows until 120 days post-calving.

At 30 days before calving, 120 pregnant Holsteins (54 heifers and 66 dry cows) from the Elsenburg herd were assigned to two nutritional treatments according to lactational number, expected calving date, LW, and milk production during the previous lactation (respectively 8697 ± 131 kg and 8650 ± 132 kg for the Control and Treatment multi-lactation group). Pre-calving heifers and cows were fed independently a similar type and level of a pre-calving concentrate, in conjunction with ad libitum intake of either un-chopped oat hay for the Control group or a partial total mixed ration (pTMR: 48% oat hay, 43% lucerne and 9% soybean oil cake meal) for the Treatment group. After calving, cows in both the Control and Treatment groups were maintained ad libitum on cultivated irrigated kikuyu-ryegrass pastures, supplemented each with a post-calving concentrate of 7 kg/day from calving until 120 days in milk (DIM).

As expected, young and still growing first lactation cows were significantly lower in pre- and post-calving LW traits compared with mature multi-lactation (>3) cows. Pre-calving LW of cows was similar between Control and Treatment in both lactation groups. Post-calving LW of the first-calf cows differed significantly between Control and Treatment, which were 488 ± 9 and 507 ± 13 kg, respectively. However, no difference was observed in post-calving LW of multi-lactation cows between Control and Treatment, which were 579 ± 10 and 579 ± 8 kg, respectively. First-calf cows that received the pre-calving oat hay-based diet showed a significant decrease in post-calving LW loss changes, LW nadir (valley), LW loss at nadir, and rate of LW loss from calving to LW nadir in comparison with their counterparts on the pre-calving pTMR-based diet, but these LW traits were similar in multi-lactation cows. Pre-calving diets did not have an effect on post-calving fertility parameters of the multi-lactation cows, whereas first-calf cows that received the Control diet recorded a significantly longer interval from calving to first service (CFS) in the subsequent lactation, in comparison with their counterparts fed the Treatment diet i.e. 117 ± 9 and 86 ± 8 days, respectively. Proportions of cows that were pregnant at 120 DIM were similar in the subsequent lactation between groups that received the pre-calving oat hay- and pTMR-based diets in both lactation groups.

In conclusion, the study showed that first-calf cows that were maintained on the pre-calf pTMR-based diet which contained high NFC and CP levels, significantly replenished the LW and shortened the CFS interval in the subsequent lactation, compared to their counterparts on a pre-calf oat hay-based diet consisting of low NFC and CP levels. However, the proportions of cows that were pregnant at 120 DIM in the subsequent lactation were similar between the two pre-calf fibre-based diets in both lactation groups. In the multi-lactation groups, the pre-calf fibre-based diet was clearly nutritionally adequate for both lactation and fertility needs. In future though, studies should further investigate different pre-calf feeding periods and nutritional strategies that involve various types and levels of energy and protein to stimulate post-calving metabolic and hormonal responses that benefit fertility.