29 March 1996

ELITE DO WELL ON GRASS

High genetic index dairy cows can perform well on low input grass-based milk production systems according to Irish research. Sue Rider reports

HIGH genetic merit cows can perform well on grass-based diets. They eat 6% more grass than their average merit contemporaries and produce higher yields of fat and protein.

Fertility performance is also similar between the two groups.

These are the early results of a trial started last year and planned to continue for several years by Irish advisory body Teagasc at its Moorepark Dairying Research Centre, Fermoy, Co Cork.

The research investigated how high genetic merit dairy cows performed under grass-based milk production (Moorepark system) relative to average genetic merit cows.

Other systems of milk production which included higher levels of concentrate and more flexible systems of grazing management were also compared for these two genetic levels (see panel).

In autumn 1994 two contrasting genetic groups of in-calf heifers were assembled at Curtins Farm, Moorepark. Control heifers (C) comprised Moorepark stock. These were mostly Dutch crosses of their own breeding. The high genetic merit stock (S) were mostly imported (Holland and France).

The pedigree index of the selected group of animals (S) was on average 45 PIN95, 12kg fat and 13kg protein higher than the control group (Table 1).

Selection heifers (S) had a lower pedigree index for fat % and a slightly lower pedigree index for protein %. Sires of animals in the control group were mainly Arend, F16 Rocket, Etazon Bowi, Shinagh Rohorst belder, Nicholas Storm and a selection of young bulls on test. Sires of selected (imported heifers) were mainly the Dutch bull Sunny Boy and French sires Sunnylodge Sammy and Ugela Bell. Control heifers have a higher PIN than the national average for first lactation animals in 1995.

In total 96 spring-calving animals were allocated to the trial, and then 16 heifers to each treatment.

Heifers were put on their respective feeding systems from early-April last year until the end of lactation. Concentrate use was much higher than planned, mainly due to the severe drought in August and September, says Pat Dillon, who ran the research.

"The grazing season lasted from early March until early December, when all animals were housed," he says. High and average merit cows within each feeding system were grazed separately in split paddocks. Both the low input and the high concentrate systems followed conventional grass management. The high grass system saw some modifications.

Pre-Calving

Both groups of heifers were on grass until late-November 1994. Before calving in February /March heifers were fed ad lib silage except for four weeks immediately before calving when they were fed 2kg of concentrates.

Pre-calving bodyweight for the control and selected group of heifers was 543 and 564kg, respectively (Table 2). Post-calving, and before turn-out to pasture in early-March, heifers were fed 9kg of concentrates plus ad lib grass silage. Average age of the animals at calving for the control and selected groups of heifers was 24.5 and 25.5 months, respectively. After turn-out concentrate feeding was reduced to 7kg a cow a day and from early-April onwards, animals were allocated to their respective feeding systems.

Feeding

"Grass production in 1995 was very erratic with a very poor grass growth in August/September due to droughts, so concentrate feeding was higher than planned as a result," says Dr Dillon. Actual concentrate feeding rates were 863kg, 1449kg and 851kg of concentrates a cow for the Moore-park, high concentrate and high grass feeding systems, respectively. Over 200kg of this concentrate was fed during the drought, he says. An extra 1.5t of silage was also fed to each cow at this time.

Milk production and grazing

High merit cows produced significantly more milk a cow (946kg) of lower fat content (-0.31%) and with a slightly lower protein content (-0.09%) than the average merit animals (Table 3). Fat and protein yield was significantly higher (+17%) for the high merit cows, mainly due to the higher milk yield.

Dr Dillon stresses that the lower protein of the high merit cows compared with control cows (-0.09%) is merely a reflection of the difference in genetic index for protein of the two groups (-0.1%) in favour of average merit cows. "There is no indication in the trial that the higher indexed animals are producing lower constituent milk because they are higher merit animals," he says.

Production results for both genetic levels for each feeding system are shown in tables 4, 5, and 6.

Milk production for the groups in both the Moorepark and high grass intake feeding systems is similar. The difference in milk production between genotypes is lowest in the high concentrate feeding system. Response to higher concentrate levels was similar for both genotypes at 0.67kg of milk a kg of extra concentrates fed.

"Throughout the grazing season the high merit cows had higher intakes of grass for similar levels of use as compared with the medium merit cows," says Dr Dillon. The selected animals required 3-6% more pasture for the same levels of utilisation. He estimates the extra grass intake to be about 6% over the total grazing season. This gives the high merit cows a 12% advantage in terms of grass feed efficiency.

But he stresses that to get the performance out of these cows requires high quality grass growth and good grazing management. "There is no point in having high merit cows if you are not going to feed them properly and if they are just going to fall down in the system."

Nitrogen use was 280kg/ha (351 units/acre) on the grazing area (Table 8).

There is no difference between the high and medium merit cows in reproductive performance (Table 7). The breeding season lasted 13 weeks and four cows of each genetic level failed to get in-calf. The difference in calving to service interval between the two genotypes was due to a difference in calving date between the groups of cows.

Pregnancy rates for first and second service for all animals was slightly lower than those normally advocated. Cows seven-days post calving are currently being blood tested and scanned to check they are cycling normally.

Immediately post-calving the high merit heifers lost 20kg more bodyweight on average and this is also evident from the change in body condition score (table 2). Average daily liveweight gain from mid-April to mid-December was similar for both genotypes (0.44 against 0.47kg a day). But the changes in body condition were not as great, with the high merit cows (+0.28 against +0.42). This was due to the difference between the two genetic levels in skeletal growth.

Genetic trends

Dr Dillon points to the marked increase in the rate of genetic improvement in dairy herds in Ireland and Britain since the mid 1980s as justification for the trial. He recognises the trebling in the rate of genetic progress in Ireland for milk fat and milk protein yields (0.4% a year to 1.1% a year) for sires born over a 10-year period (1980-1990). (UK Animal Data Centre geneticist Gordon Swanson says the average genetic progress for bulls in the UK over the past five years is at least 5%).

He sees this trend continuing for the foreseeable future with further advances in animal breeding and in milk production technology. "Such genetic progress presents new challenges to milk production systems based mainly on the efficient conversion of home-produced forage, grazed grass and silage to milk," says Dr Dillon.

This demands a compact calving pattern in spring (Feb/March) to maximise use of grass.n


Table 8: Nitrogen application rates kg/ha (units/acre) and timing

PeriodGrazing only area

(55% of farm)

Early January50 (40)

Early – late March50 (40)

Late March – mid-April50 (40)

Mid-April – early May50 (40)

Early – late May34 (27.5)

Late May – mid-June34 (27.5)

Mid-June – early July34 (27.5)

Early – late July34 (27.5)

Late July – mid-August34 (27.5)

Mid-August – early

September34 (27.5)

Early – late September34 (27.5)

Total439 (351)


Table 2: Effect of genotype on bodyweight (kg) and body condition score (CS) changes

Pre-calvingMid-AprilMid-December

LvwtConditionLvwtConditionLvwtCondition

(kg)score(kg)score(kg)score

High merit cows (S)5642.894902.436022.71

Medium merit cows (C)5433.144882.786063.20


Table 4: Moorepark feeding system

Medium meritHigh meritDifference

cows (C)cows (S)(S-C)

Milk (kg a cow)5,3036,347+1044

Fat (%)4.023.68-0.34

Protein (%)3.503.42-0.08

Fat (kg)212232+20

Protein (kg)185217+32


Table5: High concentrate feeding system

Medium meritHigh meritDifference

cows (C)cows (S)(S-C)

Milk (kg a cow)5,8126,633+821

Fat (%)4.053.79-0.26

Protein (%)3.543.44-0.10

Fat (kg)234251+17

Protein (kg)205228+23


Table 7: Fertility performance

Medium meritHigh merit

cows (C)cows (S)

% cows served – 1st three weeks9285

Calving to 1st service interval (days)7190

Services a conception1.911.82

Pregnancy rates:

1st service4654

2nd service5448

3rd service8079

Infertility rate (%)8.38.3


Table 3: Comparison of genetic levels across the three feeding systems

Medium meritHigh meritDifference

cows (C)cows (S)(S-C)

Milk (kg a cow)5,4966,441+945

Fat (%)4.063.75-0.31

Protein (%)3.533.44-0.09

Fat (kg)222241+19

Protein (kg)193222+29


Table 1: Comparison of genetic index

PINMilkFatProtein FatProtein

95(kg)(kg)(kg) (%)(%)

Selected (S)806592421-0.020.00

Control (C)35151128 0.110.05


Table 6: High grass intake system

Medium meritHigh meritDifference

cows (C)cows (S)(S-C)

Milk (kg a cow)5,3736,343+970

Fat (%)4.103.78-0.32

Protein (%)3.543.47-0.07

Fat (kg)219240+21

Protein (kg)189220+31

Selection and control line animals are fed a winter ration of ad lib grass silage plus parlour-fed concentrates.

Flor Flynn (left) herd manager of Mooreparks Curtins Farm with researcher Pat Dillon in a paddock to be grazed by high merit cows.