Researchers at Teagasc Moorepark have been investigating winter feeding options for dairy replacement heifers.
Rearing a re placement heifer from birth to calving costs €1,486. This includes costs for initial calf value, and land and labour (if these are excluded, the cost is € € 805).
Heifer rearing is the second largest expense in dairy, about 20% of total costs — a substantial investment, especially when the removal of milk quotas is considered, and dairy farmers face a more competitive environment, with increased milk price volatility and, hence, less stable farm profitability.
Ensuring the best possible development of replacement heifers is critical. Although it needs to be accomplished at low cost, heifer performance should not be compromised.
Optimum performance is influenced by realising target weights at key points, such as mating start date (MSD) at 15 months, and pre-calving.
Unfortunately, in practice, heifer rearing gets low priori-ty on Irish dairy farms, and achieving target weights is neglected by many. Reduced levels of management will result in less profit, as heifers which calve later than 24 months, are underweight and produce less milk, compared to better managed heifers.
Research Technologist Emer Kennedy reported on the Moorepark investigation in the autumn edition of Re-search, the official science publication of Teagasc.
First winter diet
Experiments at Teagasc Moorepark investigated different over-winter diets on heifer weight gain.
Results showed the choice of winter diet significantly impacts weight gain, and realisation of MSD target weight.
Feed costs account for about 80% of the total variable costs of production.
One method of reducing feed costs is sourcing lower cost feeds, and kale grazed in situ ranked as the cheapest alternative to grazed grass — and was considerably cheaper than grass silage, in a recent Teagasc study.
Kale tends to have a low neutral-detergent fibre (NDF) concentration, suggesting that feeds with a higher NDF concentration — such as grass silage — may need to be offered too, to avoid acidosis. A 20-day indoor feeding experiment at Moorepark examined feeding a 100% kale diet, in comparison with varying combinations of kale and silage. The results indicated that feeding 100% kale did not reduce rumen pH below 6.0, nor did it induce acidosis. Thus, 100% kale feeding was introduced to the tests.
First winter diets investigated, and weight gains (kg per day) achieved included:
¦ Ad libitum grass silage and 1 kg (dry matter) of concentrate/day indoors resulted in winter weight gain of 0.44kg per day and 0.68 kg from turnout to breeding.
¦ Ad lib grass silage only ( SO) indoors: 0.3kg and 0.86kg.
¦ 70% kale and 30% grass silage bales outdoors (70K): 0.47kg and 0.89kg.
¦ 100% kale outdoors (100K): 0.48kg and 0.88kg.
¦ Ad lib grass silage and 2kg DM concentrate/day (S2) indoors: winter weight gain of 0.65kg per day.
The experiments showed considerable variation in weight gains from different diets over the winter.
Kale has a high feeding value (1.05 UFL, similar to early spring grass); consequently, heifers can achieve high weight gain at a relatively low cost. Similar weight gain can be achieved with grass silage and concentrate diets.
Silage-only diets support weight gains of about 0.3kg/ heifer/day. Therefore, heifers should be well ahead of target at housing, if silage only is fed during the winter — because 0.3kg is insufficient weight gain to achieve target weight at MSD for heifers that commence the winter period at or below target weight.
Which forage crop to use? Another experiment was completed to establish if there were differences in weight gains achieved from three different forage crops and more conventional diets. The diets investigated were:
¦ Grass silage and 1kg DM concentrate/day indoors (S1).
¦ Grass silage and 2kg DM concentrate/day indoors (S2).
¦ Grazing forage kale (Maris Kestral) with grass silage bales offered as 30% of the diet outdoors (K).
¦ Grazing forage rape (Stego) with grass silage bales as 30% of the diet, outdoors (R).
¦ Grazing a rape-kale hybrid (Red Start) forage with grass silage bales offered as 30% of the diet outdoors (H).
At turnout, there was no weight difference between heifers from the S2, K, R and H treatments (279kg), but all were heavier than the S1 heifers (261kg). Thus, over-winter weight gain was least for the S1 heifers (0.38kg/ heifer/day), compared with all other treatments, which were similar (0.53kg/heifer/ day). There was no difference in the turnout body condition score (BCS) for the five winter feeding treatments.
Regardless of winter diet, similar weight gains are achieved when heifers are turned out to grass in spring. Weight gains achieved post-turnout are higher than those achieved during the winter.
This clearly indicates that heifers should be turned out to grass as soon as possible, as they can gain up to 1kg/ heifer/day at grass, compared to <0.7kg/heifer/day on their winter diet. Consequently, heifers have a greater chance of attaining their target weight with early turnout. Second winter diet
Many research studies have shown a positive relationship between body weight at calving and first lactation milk yield. An experiment was undertaken to investigate the effect of winter diet on prepartum weight gain of replacement dairy heifers, and to establish the effect of prepartum feeding treatment on post-partum milk production.
The treatments were:
¦ Silage only indoors (SO).
¦ Silage and 2kg concentrate/day for 46 days, followed by silage only indoors (SC).
¦ Grazing forage kale with grass silage bales at an inclusion rate of 30% in the diet, outdoors (70K) ¦ 100% kale grazing (100K).
Daily weight gain was similar for the SC and 70K treat-ments (1.1kg/heifer/day). Weight gain was lower for the SO treatment (0.96kg/heifer/ day), and was further reduced on the 100 K treatment (0.78kg/heifer/day). At the end of the winter period, BCS was greatest for the SO and SC animals (3.47), significant-ly lower for the 70K animals (3.25), and lowest for the 100K animals (3.09).
There was no difference between treatments in cumulative milk yield (3,656kg) or milk solids yield (273kg) for the first 29 weeks of lactation. There was no difference between treatments in average lactation fat, protein and lactose concentration (4.10, 3.38 and 4.70%, respectively).
Average body weight throughout the first 29 weeks of lactation was also similar between treatments (439kg). Average BCS of animals from the 100K treatment was lower (2.86) than in the SC and SO animals (3.0), but similar to the 70K animals (2.93).
There was no difference in average BCS between the SC, SO and 70K treatments (2.98).
The trails outlined the weight gains that can be expected from winter diets for replacement dairy heifers.
The diet offered should en-sure that heifers attain key target weight, such as at MSD and pre-calving. Thus, heifers should be regularly weighed, and appropriate first and second winter diets chosen to ensure lifetime performance is optimised when they reach the lactating herd.
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