THE EFFECTS ON DAIRY COWS OF GRAZING PASTURE CONTAINING HIGH LEVELS OF NITRATE-NITROGEN

Two paddocks each received a total of 412 kg N/ha (371 lb/ac) between April and July in four equal applications. The paddocks were grazed four times for four days by two groups of 5 Friesian cows starting 14 and 21 days after each N applica tion. The nitrate-N content of the herbage DM reached a peak of 0·76 % in the third grazing 14 days after N application. There was a significant (P < 0·001) correlation (r =0·67) between water soluble carbohydrates and nitrate-N in the herbage DM. No marked changes occurred in eitber the methaemoglobin or packed cell volume of the blood samples from either group. No detrimental effects on animal health or production were recorded during the experiment.     

THE INFLUENCE OF SUPPLEMENTARY FEEDING ON THE HERBAGE INTAKE AND GRAZING BEHAVIOUR OF DRY COWS

The herbage intake and grazing behaviour of 4 dry cows on autumn grass receiving 2, 4, 6 or 8 kg concentrates/day, was assessed in a 4×4 Latin Square experiment. Total OM intake increased from 11±5 kg/day with 2 kg concentrates to 13±6 kg/day with 8 kg concentrates. The average supplementary effect was 0±46 kg increase in OM intake/kg OM fed as concentrates. Minutes per day spent grazing decreased from 495 with 2 kg concentrates to 359 with 8 kg. The mean decline was 22 min./kg concentrates or 28 min./kg OM in concentrates eaten. Herbage was eaten at an average rate of 47 min./kg OM.     

THE AUTOMATIC RECORDING OF THE GRAZING BEHAVIOUR OF DAIRY COWS

A technique for the automatic recording of the grazing behaviour of dairy cows was investigated, using ‘Vibracorders’ which transmit grazing movement via a pendulum and stylus to a 24 h recording chart. The total labour input was 2 h/day for 6 cows, which gave 144 h of results. In 2 months, 3312 h of recording were obtained. Total grazing time per cow in 24 h was 559 min. on a rigid rotational system of grazing and 638 min. on a system of set stocking. Grazing time was significantly and negatively related to the yield of available herbage DM. It is concluded that if the Vibracorders are sealed and fitted correctly, they are simple, reliable and accurate instruments for automatically measuring the grazing behaviour of dairy cows.     

SOME ESTIMATES OF THE AREAS OF PASTURE FOULED BY THE EXCRETA OF DAIRY COWS

Observations were made of the areas of herbage receiving the faeces of grazing dairy cattle and of the areas and relative palatability of herbage whose growth was affected by faeces and urine. The average area covered by faeces was 7·3 sq. ft./cow/day. Faeces dropped during grazing had a negligible affect on the utilization of herbage at that grazing, but each dung-pat probably affected the growth and palatability of an area of herbage about six times as great at the next grazing. The area of herbage whose growth was affected by urine was equal to that affected by faeces, but unlike faeces, urine improved the palatability of the herbage to dairy cows. The data were used to calculate approximate areas of herbage likely to be affected by excreta at different levels of stocking, and it appeared that excreta return plant nutrients to a given pasture acreage more quickly than some other estimates suggest.     

THE INTAKE OF DRINKING WATER BY GRAZING DAIRY COWS. THE EFFECT OF WATER AVAILABILITY

In a 16-week grazing experiment with six spring-calved Ayrshire cows, drinking water was available to the animals in three different ways, and the effect on milk prodnction was studied. The water was available from a water howl in the cowshed for 2.8 h/day in Treatment A, from a trough in the field for 21.2h/day in Treatment B, and from hoth sources for a total of 24 h/day in Treatment C. The cows on all treatments were grazed in individual plots of intensively-managed perennial ryegrass, stocked at the rate of 1 cow/0.22 ha (0.54 ac). The mean daily intakes of drinking water were 10.1, 15.3 and 15.5 kg (2.23, 3.37 and 3.42 gal)/cow, and the mean daily milk yields were 17.0, 17.2 and 16.8 kg (37.5, 37.9 and 37.0 lb)/cow in Treatments A, B and C, respectively; milk yields were not significantly different The herbage had an average DM content of 17.3%, and contained 19.6% crude protein and 66.5% digestible organic matter in the DM. The weight of water drunk was significantly and positively related to the DM percentage of the herbage, the air temperature and the daily hours of sunshine, and negatively related to daily rainfall. It is concluded that when dairy cows are grazing leafy herbage of high digestibility as their sole feed, the time during which drinking water is available may safely be restricted.     

THE OUTDOOR REARING OF AYRSHIRE CALVES ON PASTURE WITH AND WITHOUT SUPPLEMENTARY FEEDING

An experiment conducted in south-west Scotland during 1956 and 1957 to investigate an outdoor method of rearing calves on pasture, with and without supplementary food, is described.
Twenty-four Ayrshire bull calves were put on pasture at 2 weeks of age and received an average of 37 gallons of whole milk up to the time they were weaned at 8 weeks old. Twelve of the calves received no supplementary feeding, but the other twelve each ate 257 lb. of a meal containing oats, linseed cake, flaked maize and fish meal from their 3rd to their 20th week.
The calves were moved around a series of plots (0.4 acre) which yielded an average of 1400 lb. of dry matter per acre at each grazing. The mean crude protein of the herbage dry matter was 17.4% in 1956 and 14.1% in 1957.
The mean daily liveweight-gains of the calves from birth to 20 weeks of age were 1.05 lb. for the unsupplemented calves and 1.14 lb. for the supplemented ones—a non-significant difference, as was also the difference between the mean increases in belly-girth measurements of the two groups.
Parasitic infestation of the two groups was extremely low and 83% of all faeces samples examined contained no worm eggs.
The latest-born calves made the poorest liveweight gains.
The outdoor rearing of calves is discussed.     

THE INFLUENCE OF GRAZING "IMMUNE COWS" ON THE LEVEL OF DICTYOCAULUS VIVIPARUS INFECTION ON PASTURE

At the Agricultural Research Institute, Hillsborough, Northern Ireland, during September and October, 1958, a field which was naturally infected with Dictyocaulus viviparus (lungworm) larvae was divided and one part was intensively grazed by cows which were not excreting lungworm larvae while the other part remained unstocked. Records were kept of the available herbage, total dry matter and the numbers of larvae on both areas. Grazing resulted in a marked reducuon of the larval numbers which was greater, in proportion, than that of the amount or herbage. Although severe grazing did not remove the infection, it so accelerated the decline in numbers that an infection level of one larva per lb. herbage was reached 7 weeks earlier on the grazed than on the ungrazed area. The herbage in both areas showed no larvae about 4 months after infected faeces were last voided on to it.     

THE EFFECT OF INCLUDING DRIED GRASS IN THE SUPPLEMENT GIVEN TO LACTATING COWS AT PASTURE

An investigation into the effect of including dried grass in the supplement given to dairy cows at pasture is reported. Supplements containing 0, 50 and 100% dried grass were used in the investigation which was carried out in two parts. In the first part 12 high-yielding cows with unrestricted access to pasture were used in an experiment with a change over design to assess the effects of feeding 5 kg/day of each supplement on milk yield and composition. In the second part 8 steers, housed in stalls and given cut herbage from the same sward as that grazed hy the cows, were used in a change over experiment to assess the effects of the three supplements on herhage and total DM intake. No significant differences in milk yield between supplements were ohtained, the mean yields being 23·9, 24·5 and 23·9 kg/day for the supplements containing 0, 50 and 100% dried grass, respectively. Milk composition was also not significantly affected by including dried grass in the supplement. In the indoor feeding trial using the steers, the addition of 3·5 kg DM from the supplement resulted in an increase in total DM intake of only 1·3 kg/day. There was no significant difference hetween supplements on herbage and total DM intake.     

REMOVAL OF THE EFFECTS OF UNEVEN GRAZING IN PASTURE EXPERIMENTS

An experiment is described in which uneven grazing by sheep introduced a bias in a white clover variety trial. The data were adjusted by covariance, using as the independent variable the position of the plots within the paddocks.
Attention is drawn to the errors that may result from uneven grazing and a comparison is made with errors due to transference of fertility. Means of avoiding similar occurrences are suggested.     

INTENSIVE SET-STOCKING OF DAIRY COWS

Farm-scale trials with Ayrshire dairy cows were conducted in South-West Scotland over two seasons to compare set-stocking and paddock grazing at similar stocking rates and N fertilizer rates. At a stocking rate of 1±9–2±0 cows/ac throughout the grazing season and a fertilizer N rate of about 400 units/ac, milk production per head from set-stocked cows was equal to that from paddock-grazed cows. No health problems arose as a result of applying fertilizer to the fields which were set-stocked. These trials hare established that set-stocking is a viable system for the intensive management of dairy cows on grassland in the UK, but further work is necessary to determine whether paddock-grazing has a higher potential for milk production than set-stocking.     

THE EFFECTS OF WINTER GRAZING ON SUBSEQUENT PRODUCTION FROM PASTURE

The eflFects of various systems of winter-grazing management on pasture production in the following spring and summer were studied in four trials in the Pentland Hills, Scotland. Winter grazing reduced the yield of herbage in spring, but growth in May and June was primarily influenced by the level of nitrogen application in spring, irrespective of winter-grazing treatments.     

DAIRY PRODUCTION FROM PASTURE; A COMPARISON OF TWO METHODS OF CONTROLLED GRAZING AT TWO RATES OF STOCKING

An experiment was started in 1957 that compared the production from dairy cows on daily strip-folding with that from a system of rotational grazing where the cows were given a fresh allocation of pasture about once or twice a week. Management was so arranged that equal areas of pasture were grazed off by the same number of cows in a similar period of time. The experiment was carried out at two rates of stocking, one about 20% greater than the other, the lower rate considered to be equivalent to good close folding practice and the higher rate therefore somewhat restrictive. No supplementary food was given during the grazing season.
At the high rate of stocking, rotational grazing gave an average milk yield of 40 lb./cow/day whilst daily strip-folding yielded 38 lb./cow/day. At the low rate of stocking production was 42 lb./cow/day for both methods.
At the high rate milk yield/acre from the rotational grazing was 1007 and from the strip-folding 977 gals. At the low rate comparable results were 881 and 874 gals.
There was no general trend in yield per cow or per acre in favour of either the rotational grazing or daily strip-folding systems of management. Increasing cow days/acre by 21% decreased yield/cow/day by 7% but significantly increased milk yield/acre, by 13%.     

A STUDY OF THE INTAKE OF DRINKING WATER BY DAIRY COWS AT GRASS

The average daily intake of drinking water of two groups of 10 spring-calved Ayrshire cows, one gronp on a paddock and the other on a Wye College system of grazing, was measured on 4 days/week for 20 weeks. Trends in water intake were similar on both systems, the average daily intake being 23.0 ±8.5 kg (5.1 ± 1.9 gal)/cow. The average DM content of the herbage was 17.8% and the mean air temperature 134°C (56 1°F). The weight of water drunk was positively related to the daily milk yield and the DM percentage of the herbage, and negatively related to daily rainfall and relative humidity. All of these relationships were significant. Possible changes in the provision of water for dairy cows at grass are discussed.