The View from Teagasc: Researchers at Teagasc Moorepark have been investigating a number of winter feeding options for dairy replacement heifers.

The replacement heifers born each year are the engine of the future dairy herd. The cost of rearing a replacement heifer (from birth to calving) is €€1,486. This includes a cost for an initial value of the calf and a charge for land and labour. When these costs are excluded the cost is €€805. Heifer rearing is the second largest expense in the dairy system, accounting for approximately 20 per cent of total costs.

This equates to quite a substantial investment, especially when the removal of milk quotas is considered and dairy farmers will 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 and, although it needs to be accomplished at low cost, heifer performance should not be compromised. Optimum performance from the dairy herd during the rearing of replacement heifers is influenced by realising target weights at key points, such as at mating start date (MSD) at 15 months of age and pre-calving.

In practice, heifer rearing receives low priority on Irish dairy farms and achieving target weights is neglected by many. Reduced levels of management will result in a lesser profit, as heifers may calve later than 24 months, be underweight and produce less milk compared to better managed heifers.

Diet options during the first winter

Over the past number of years, experiments have been carried out at Teagasc Moorepark to investigate the effect of offering different over-winter diets on heifer weight gain. Results have shown that the winter diet offered to heifers significantly impacts the weight gain achieved and their realisation of target weight at MSD.

However, feed costs account for approximately 80 per cent of the total variable costs associated with costs of production. One of the methods of reducing feed costs in particular, is by sourcing lower cost feeds 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 (>500 g/kg DM) – such as grass silage – may need to be offered in order to avoid acidosis. A short-term (20-day) indoor feeding experiment conducted at Teagasc Moorepark examined the effect of feeding a 100% kale diet in comparison to varying combinations of a kale and silage diet. The results of the experiment reported that feeding a 100% kale diet did not reduce rumen pH below 6.0 nor did it induce acidosis. Thus, 100 per cent kale feeding treatments were introduced to the experiments.

The diets investigated included:
• indoors offered ad libitum grass silage and 1 kg DM concentrate/day (S1);
• indoors offered ad libitum grass silage and 2 kg DM concentrate/day (S2);
• indoors offered ad libitum grass silage only (SO);
• outdoors on an out-wintering pad offered ad libitum grass silage and 1.5 kg DM concentrate/day (OWP);
• outdoors offered 70% kale and 30% grass silage bales (70K);
• outdoors offered 100% kale (100K)

Table 1. Effect of diet on weight gain at different periods (kg/heifer/day).
Weight gain (kg/heifer/day) SO S1 S2 70K 100K
Winter weight gain 0.30 0.44 0.65 0.47 0.48
Weight gain from turnout to breeding 0.86 0.68 – 0.89 0.88

The Moorepark experiments have shown that considerable variation exists in the weight gain achieved from different diets offered over the winter (Table 1). Kale has a high feeding value (1.05 UFL – similar to early spring grass); consequently heifers can achieve high levels of weight gain at a relatively low cost. Similar levels of weight gain can be achieved with grass silage and concentrate diets. Silage-only diets support weight gains of approximately 0.30 kg/heifer/day. Therefore, heifers should be well ahead of target at housing if silage only is being used during the winter as 0.30 kg/day 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:
• indoors offered grass silage and 1 kg DM concentrate/day (S1),
• indoors offered grass silage and 2 kg DM concentrate/day (S2),
• outdoors grazing forage kale (cv. Maris Kestral) in conjunction with grass silage bales which were offered as 30% of the diet (K),
• outdoors grazing forage rape (cv. Stego) in conjunction with grass silage bales which were offered as 30% of the diet (R),
• outdoors grazing a rape x kale hybrid (cv. Red Start) forage in conjunction with grass silage bales which were offered as 30% of the diet (H).

At turnout there was no weight difference between heifers from the S2, K, R and H treatments (279 kg) but all treatments were heavier than the S1 heifers (261 kg). Thus, over-winter weight gain was least for the S1 heifers (0.38 kg/heifer/day) when compared to all other treatments which were similar (0.53 kg/heifer/day). There was no difference in the turnout body condition score (BCS) for the five winter feeding treatments.

Early turnout
Regardless of diet offered over the winter, 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 1 kg/heifer/day at grass compared to <0.70 kg/heifer/day while on their winter diet (Table 1).

Consequently, heifers have a greater chance of attaining their target weight with early turnout. Diet during the second winter. Many 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 pre-partum weight gain of replacement dairy heifers, and, establish the effect of pre-partum feeding treatment on post-partum milk production performance.

The treatments were:
• indoors offered a silage only diet for the duration of the experiment (SO),
• indoors offered silage and 2kg concentrate/day for 46 days followed by a silage only diet (SC),
• outdoors grazing forage kale in conjunction with grass silage bales at an inclusion rate of 30% in the diet (70K),
• outdoors grazing a 100% forage kale diet (100K).

Following the winter period daily weight gain was similar for the SC and 70K treatments (1.10 kg/heifer/day), weight gain was lower for the SO treatment (0.96 kg/heifer/day), and weight gain was further reduced on the 100K treatment (0.78 kg/heifer/day). At the end of the winter period, BCS was greatest for the SO and SC animals (3.47), significantly 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 (3,656 kg) or milk solids yield (273 kg) 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 (439 kg). Average BCS of animals from the 100K treatment was lower (2.86) than that of the SC and SO animals (3.00) but was not different to the 70K animals (2.93).
There was no difference in average BCS between the SC, SO and 70K treatments (2.98).

This series of studies outlines the weight gains that can be expected from a number of winter diets offered to replacement dairy heifers. The diet offered should however ensure that heifers attain target weight at key time points, for example, MSD and pre-calving. Thus, heifers should be regularly weighed and an appropriate diet chosen for the winter months during both the first and second winter to ensure that lifetime performance is optimised when they reach the lactating herd.

By Emer Kennedy, Research Technologist, Animal & Grassland Research and Innovation Centre at Teagasc Moorepark
This feature first appeared in Teagasc’s TResearch publication, which is available here.

Image O’Gorman Photography