Peripheral and central control of food intake

To either increase or decrease body weight of poultry, an understanding of food intake regulation is essential. Although it is advantageous to increase food intake in market birds, it is desirable to decrease intake in breeders. Recent studies have shown that the digestive tract, liver, and brain are all involved in food intake regulation. In this review, the role of various neurotransmitters and metabolic substrates in food intake regulation, both within the central nervous system as well as in the periphery, is discussed. In addition, how the strain of the bird or the physiological state of the animal influences the response to various compounds is discussed.

Egg production efficiency in dwarf lines selected for high and low body weight as influenced by feed restriction

Hens from dwarf Single Comb White Leghorn lines selected for four generations for high (H) and low (L) body weight (BW) plus randombred controls (C), sixty birds per line, were placed in cages at 18 wk of age and randomly assigned to either a full-fed (FF) or restricted-fed (R) (10 percent less than FF group) treatment. Birds received a layer ration having 16% protein and 2,816 kcal/kg metabolizable energy. Water was provided ad libitum. Individual BW and egg weights (EW) were obtained, and daily feed intake (DFI), egg production (EP), performance efficiency (PE) [egg mass (EM) per BW], and feed efficiency (FE) [EM/DFI] were calculated for 28-day periods from 18 to 41 wk of age. There were significant line, treatment, and age effects and line by age interactions for BW, EW, EM, DFI, and PE; FE was significantly influenced by age. There were significant treatment by age interactions for BW, DFI, and FE. Feed intake, BW, and EW were greatest for FFH hens and increased in all lines with age. Maximum EM occurred during 30 to 33 wk for RH and RL hens, during 34 to 37 wk for FFH, and during 38 to 41 wk for FFL. Maximum PE occurred during peak EP. Maximum FE for FFH and FFL occurred during 26 to 29 wk and during 30 to 33 wk for RH and RL. Data for C hens were intermediate to the other lines. Feed efficiency was improved by restriction for L hens from 26 to 33 wk and for H hens from 26 to 33 wk and for H hens from 26 to 41 wk of age.

Production performance of white Leghorn layers limited fed

Three trials were conducted to determine if the age at start of limited feeding or the amount of time laying hens were given to consume feed could be used to reduce feed intake without affecting egg weight (EW) or egg production. The age at start of limiting feed did not affect hen-day egg production (HDEP) or EW in any trial. In Trial 2, a significant difference in HDEP due to feeding times at 26 weeks of age was observed. Laying hens fed 7 hr/day at 26 weeks of age had a significantly lower HDEP than any other feeding time. Limited feeding in Trials 1 and 2 significantly decreased feed consumption, body weight gain (WG), and EW when compared with laying hens fed ad libitum. No difference in HDEP or EW was observed due to limited feeding in Trial 3. Laying hens fed 9 or 10 hr/day gained significantly less weight than laying hens fed ad libitum (Trial 3). Limited feeding did not improve feed efficiency in any trial. No consistent improvement in mortality could be attributed to limited feeding.

The response of liver enzymes to feed restriction and subsequent ad lib. feeding in the laying hen

1. The effects of restricted feeding, and ad lib. feeding following food restriction, on hepatic carbohydrate and lipid metabolism in the laying hen were studied. 2. The birds were allocated to four groups and given either 92, 84 or 75 g/d or allowed ad lib. access to food. 3. Food restriction significantly reduced liver total lipid content compared with ad lib.-fed control birds and this was reflected in reduced hepatic lipogenic enzyme activities. 4. When birds from the restricted regimens were allowed free access to food they initially consumed more food than the control group but after 2 weeks of ad lib. feeding the food consumptions of the birds in all the groups were similar. 5. Concomitant with the increase in food intake there were also increases in liver lipid content and hepatic lipogenic enzyme activities. After 18 d of ad lib. feeding these measurements were similar in the previously restricted birds and the ad lib.-fed control group. 6. Despite these effects on lipid metabolism, food restrictio, and the subsequent release from food restriction, had no significant effects on the specific activities of the glycolytic enzymes examined. 7. Although there were large increases in liver lipid content following release from feed restriction no birds died from, or showed any of the symptoms of, fatty liver-haemorrhagic syndrome. This suggests that, in the absence of any other factor which may be involved in the syndrome, these high liver lipid contents were not, alone, sufficient to cause FLHS. The results also indicate that free access to food following food restriction is unlikely to be a major factor in initiating the syndrome.

Various types of diets, sources of energy, and positive energy balance in the induction of fatty liver hemorrhagic syndrome

Adult female chickens were force-fed a corn-soy base diet at 150% of the daily amount consumed by those allowed the same diet ad libitum. Other hens were force-fed diets isocaloric to the 150% group just mentioned, but diet composition was adjusted so that 2/3 of the metabolizable energy (M.E.) came from the corn-soy diet and 1/3 from either corn oil or glucose; or force-fed a low energy diet accounting for 2/3 of the M.E. and corn oil 1/3 of M.E., or a purified diet accounting for all M.E. Fatty liver-hemorrhagic syndrome (FLHS) was induced in all force-fed groups with only the low energy diet plus corn oil having produced a significantly lower score for FLHS. However, the livers from the hens of the latter group had as much lipid, and the hens gained at least as much weight as those in other force-fed groups. During the third week of the experiment M.E. was determined along with a partition of energy among eggs, basal metabolism, body weight gain, and subsistance plus heat increment (H.I). The data showed that the hens force-fed corn oil had lower H.I. values indicative of associative dynamic action of fats at a plane of nutrition above normal. The data revealed that various types of diets and sources of energy in excess can induce FLHS, and this is discussed in terms of FLHS arising out of a positive energy balance.