Time of lay in hens exposed to intermittent lighting

1. Two short-term trials are described in which laying hens were exposed to 8 h light followed by 8 one-min pulses of light at hourly intervals followed by 8 h darkness (8L:8i:8D). The effect of varying the intensity of illumination during the one-min pulses and the effect of placing the intermittent lighting before the 8 h photoperiod (8i:8L:8D), were studied. 2. Normal egg production was maintained by the 8L:8i:8D system when the light pulses were at 20 lux, but not at 5 lux. This suggests a minimum threshold for illumination with short light pulses higher than that needed for continuous lighting. 3. Time of lay under 8L:8i:8D was the same as with 8L:16D in relation to the beginning and ending of the 8 h main photoperiod, but with 8i:8L:8D mean time of lay was 2 to 3 h earlier. Thus the hourly pulses caused a phase advance when placed before the normal photoperiod but did not cause a phase delay when placed after the normal photoperiod.     

The determination of the methionine requirement of laying pullets by a diet dilution technique

A method for the determination of amino acid requirements of laying hens is described. This involves the dilution of a high protein “ summit” diet with an isocaloric nitrogen‐free mixture. By ensuring that the amino acid to be assayed is first‐limiting in the summit diet, the response to dilution can be interpreted as a response to a single amino acid.

The method is applied to the determination of methionine requirement and it is shown that the response to methionine obtained is virtually independent of the protein level of the diet and is not influenced by direct effects of the dilution mixture.

From the results of the present and other published experiments, the “ available “ methionine required for maximum egg yield of pullets in the early stages of lay is estimated to be 275 mg per bird per day.     

Disease prevalence in Georgia turkey flocks in 1986

Disease prevalence in turkeys was estimated by totaling the flock size of necropsy cases submitted to the University of Georgia in 1986 for each disease reported and comparing it with the population at risk. Fowl cholera was the most prevalent disease in both commercial tom flocks (18.0%) and breeder hen flocks (14.7%). Prevalence of colibacillosis was 15.9% in commercial tom flocks, and prevalence of aspergillosis was 8.5% in commercial tom and 4.9% in breeder hen flocks.     

Protection of cattle against heartwater in Botswana: comparative efficacy of different methods against natural and blood-derived challenges

Five groups of Tswana-cross castrated male cattle between 20 and 30 months of age (a total of 158 animals) were transported from a ranch in a heartwater-free area of south Botswana to a feedlot near Gaborone in the east of Botswana where heartwater is endemic. On arrival, one group was vaccinated intravenously with the Onderstepoort sheep blood heartwater vaccine, one group was vaccinated intravenously with the new Onderstepoort tick-derived heartwater vaccine and a third group was vaccinated subcutaneously with this tick-derived vaccine. Vaccine reactions were blocked with long acting oxytetracycline on the first day of fever. A fourth group had a series of injections of long acting oxytetracycline on days 0, 7, 14 and 21 after arrival, and a fifth served as untreated controls. The animals remained at the feedlot for 65 days during which time they faced a low level of challenge by Amblyomma hebraeum ticks. None contracted heartwater and so they were then challenged, together with a further group of control cattle, with a dose of the sheep blood vaccine. Some animals in all groups had severe heartwater reactions and died despite therapy, but 76.7 per cent, 64.5 per cent and 74.3 per cent of the cattle in the blood vaccine, intravenous tick vaccine and long acting oxytetracycline groups respectively were resistant to challenge, compared with 48.3 per cent of the subcutaneous tick vaccine group and 36.4 per cent of the controls. It was concluded that intravenous vaccination of susceptible adult cattle with either the blood or the tick-derived vaccine needs careful monitoring in the month after vaccination and does not necessarily result in immune animals.(ABSTRACT TRUNCATED AT 250 WORDS)     

Book review

The Care and Management of Farm Animals, 2nd edition, edited by W. N. Scott. Baillière Tindall, 1978. 254 pp. Price £7.95. ISBN D 7020 06823.