Dairy cows giving birth to heifers have higher yields. US trials featuring 2.39 million lactations from 1.49 million cattle concluded that those calving heifers produced an average 980lbs more milk over their first two lactations. “These findings demonstrate that a cow’s nurturing signals start at conception and biased milk production is programmed during pregnancy. A cow favours her heifer with more milk for better growth.

Fig 1: Comparison of serum IgG concentrations between colostrum with varying bacteria levels

“That’s lactocrine hypothesis programming: a cow sends signals via her colostrum which say she wants her calf to grow and be healthy,” he said. “Whilst noted for providing immunoglobulins (IgG) to establish passive immunity, colostrum also contains a complex mix of nutrients and non-nutrients which instruct the calf how to realise her genetic potential.” They include insulin which drives glucose out of the gut and into the digestive system, prolactin, IGF-1 which drives protein synthesis, 17 Estradiol, a steroid for growth promotion and growth hormone.

Whilst research in to understanding colostrum’s function is currently ongoing, trials have so far proven that the mix of components encourage

- gut maturation - more developed function tissue and more enzymes encourage greater digestibility, absorption capacity and uptake

- a supply of hormones that enhance absorption

- and an uptake of hormones which altered set points for feed uptake, and possibly feed efficiency.

“US trials which extended colostrum feeding beyond the first 24 hours to the first four days concluded that glucose uptake increased by almost 100%, plasma glucagon and plasma protein levels were higher and plasma urea lower.

“Further US trials have concluded that colostrum’s components can impact on pre and post weaning feed efficiency. Colostrum has also been proven to influence feed intake regulation or satiety post weaning and the combination of the two effects maybe for life. In other words, the lactocrine hypothesis proposes that some factors in colostrum may permanently affect future calf performance such as growth, efficiency or even future milk production.”

Setting the growth targets

Be proactive. Set growth targets to in order to optimise first and subsequent lactation milk yields, was the message from Cornell University’s Prof Mike Van Amburgh. “If your heifers fail to achieve these targets by first breeding, then they’ll never ever catch up,” he said.

“Younger animals at first breeding are reproductively more efficient, they are able to do more work so you’ll get more days of milk and they’ll have fewer issues. Basically these younger animals do not cost as much to rear to first lactation and they result in being more profitable. Furthermore, you’ll need fewer annual replacements to maintain herd size.”

Table 1: Essential growth targets
Birth to weaning	Double body weight
Puberty	45% mature weight
Breeding and pregnancy	55 – 60% mature weight
First lactation post calving body weight	82 – 85% mature weight

Source: Van Amburgh

“Your goal is to achieve 82% of mature size to achieve 80% of mature cow milk yield. For mature weight, it’s determined at the middle of the third and fourth lactation, 80 to 200 days in milk on healthy cows, not culls.” See Table 2 for target weights.

Table 2: Target weight for any mature size of cow
		Mature body weight kg
		500	650	800
	% mature weight	Target breeding weight kg
Pregnancy	55	275	358	440
First calving	82	410	533	656
Second calving	92	460	598	736
Third calving	96	480	624	768

Source: Van Amburgh

Pre-weaning impact on milk yield

Nutrition and subsequent growth rate prior to weaning has a much more direct and significant effect on milk yield than genetic selection for production according to US trials.

“Whilst genetic selection within the herds being evaluated yielded just 68 – 115kg of additional milk per lactation, pre-weaning calf nutrition and management yielded between four and eight times more milk,” said Prof Mike Van Amburgh, of Cornell University. “That means when you feed for more nutrient supply above maintenance, then you are actually setting the calf up to be a better lifetime milk producer.

Staying healthy: pre-weaned calves which avoided a health check achieved an additional 780kg milk yield compared with those suffering diarrhoea, according to US trials.

The pre-weaned calves suffering diarrhoea proved to be very sensitive to intakes compared with healthy ones. Feed intakes were reduced consequently less protein was available for protein accretion. Growth rates reduced when calves suffered diarrhoea by 30g/day and where treatment was administered overall growth was 50g/day less when compared to healthy calves. The stunted growth period was compounded by the fact it takes two to three weeks for recovery and resuming to normal feed intakes.

Colostrum management

Colostrum quality is determined by its immunoglobulin (IgG) content which is absolutely vital for future health, according to Teagasc’s Dr Emer Kennedy. However as few as 33% of calves are getting enough, or what’s referred to as adequate passive transfer (ATP), according the latest All Ireland Disease Survey. ATP is influenced by colostrum quality, timing of feeding and volume

“Strictly speaking, only the first milking is colostrum; it contains approximately 120 IgG g/l, after which IgG levels plummet by over 50%. The quality threshold is over 50mg/ml and by day three, they’ve tailed off,” she said.

Three main factors affect colostrum quality

Parity: older cows have more concentrated colostrum

Time interval: nine hours after calving the antibodies become diluted

Month of calving: Apr/May spring block calving cows have relatively low levels due to a very long dry period on grass silage and they already maybe suffering from a subclinical disorder

Storage

“Collect and store colostrum in clean containers, refrigerate within six hours of collection – a period when bacterial growth is highest, store for up to 48 hours and freeze for up to 12 months.”

Storage: Teagasc R&D findings

Colostrum which has been pasteurised, is fresh or stored at 4^oC over a 48 hour period retained acceptable IgG levels. In comparison, colostrum stored at higher temperatures of 13^oC and over, IgG levels fell to unacceptable levels due to bacteria binding to the antibodies and reducing their effectivity. (See Fig 1)

Getting the economics right

Cost of rearing a heifer replacement in a forage based spring block calving herd amounts to £1,100. However, there is serious under rearing of over 40% of all Irish heifer replacements; just 55% of heifers born in to Irish dairy herds calve between 22 to 26 months, whilst 25% fail to make it to calving, explained Teagasc’s John Maher. “We have awful lot of work to do,” he said.

“Heifers must be frequently weighed, and if you’ve yet to invest in scales, then the cost if equivalent to just one replacement heifer.”

Weight at first breeding is much more important than age at first breeding, according to a Teagasc analysis of 48 dairy units and 900 animals.

Optimum target replacement weight at first breeding 330kg (320 - 340kg)
Weight at first breeding	< 290kg	304kg	330kg	>343kg
Profit/ha (€)	916	975	1,083	892
Farm profit (,000 €)	37	39	43	36

Source: Teagasc

Heavier heifers demonstrated better reproductive performance, and improved milk solids yield over three lactations (+30kg milk solids per lactation).

Heifer target weights
	Holstein Friesian	Jersey cross
Six months (kg)	170	150
First breeding (kg)	330	295
Pre calving	550	490

Source: Teagasc

“Birth to breeding is the most important half of rearing a replacement and the major down fall area is grazing. Heifers are far too often given the worst grass,” he said.

First season at grass: target 0.7kg/day liveweight gain. Graze the heifers the same quality of grass as the heifers; implement a parasite control strategy.

First winter housing period: feed quality forage, 18-19% CP diet; separate the lighter animals and give preferential treatment.

Turnout to breeding: start grazing early on high quality grass to achieve high liveweight gains and acclimatise pre first service; turn out the lighter heifers first.

Feed for growth

Make milk feed excellence mandatory; it’s vital to contributing to a successful business, said Volac’s Niall Jaggan.

“Heifers’ average age at first calving is the measure of that success. Don’t be afraid to breed from your heifers earlier than usual, if they reach target weight sooner. We have massively underestimated our heifers’ potential.

“Target 24 months age at first calving and the cost of rearing a heifer will breakeven half way through the first half of her second lactation. She will also achieve 10 months more positive production than one calving at 30 months who won’t break even until well in to her third lactation.

“That’s not all, heifers calving at 24 months have better fertility, they have higher milk yields and have the highest survival rate over a five year period, and consequently fewer replacements will be required.” See Table 1.

Table 1: Age at first calving and impact on lifetime performance
	Age at First Calving
	23 – 25 months	26 – 30 months	Over 30 months
First lactation; days to conception	117	137	170
Second lactation; days to conception	111	133	144
Total five year milk yield (kgs)	22,477	20,605	15,777
% life spent in milk in first five years	45%	40%	34%
% cows calving at three	70%	59%	50%

Source: RVC

Contract rearing heifer replacements

20% of Ireland’s dairy farms will be facing scale or stocking rate challenges by 2020 as a direct result of national herd expansion. One solution is contract heifer rearing at a current estimated cost of £1,100 a head, including fixed plus variable costs, said Teagasc’s George Ramsbottom who offered the following guidelines.

Establish the right partnership; selecting the right person is the most important factor influencing the operation’s success. The rearer must be trustworthy, communications are vital - both before establishing the agreement and at frequent intervals afterwards.

Establish your own price, considerable variation exists between units.

Establish a health plan with your vet that is specific to your own farm; disease is the biggest risk factor associated with contract heifer rearing. If more than one herd of replacements is present on a farm, then carefully agreed precautions must be in place.

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