Thesis (MScAgric)--University of Stellenbosch, 2000 / ENGLISH ABSTRACT: A flock of 500 Hybro broiler breeders were employed to study the effect of different levels of protein and energy on production and body composition. The daily lysine intake of the birds were 900, 1050, 1200 and 1350 mg respectively, each fed in diets with a daily energy intake of 1800 and 2000 kJ ME to provide a 4 x 2 factorial design. Lysine was used as the reference amino acid in the experiment and all other amino acids were kept in a constant ratio in every experimental diet. The total production was divided into 3 periods of 13 weeks each (week 23 - 35; week 36 - 48 and week 49 - 61) to determine the effect of the treatments over time. Production was evaluated by hen day production; egg weight (g/egg); egg mass (g/day); fertility; hatchability; chicks/hen/week; feed conversion and day old chick weight. Hen day production was significantly (P < 0,05) lower at the high energy intake for period week 49 to 61. Energy and protein levels significantly increased egg weight. Effect of protein was consistent during all three periods of production. Egg mass output had a significant (P < 0,05) response to increasing levels of protein for the total period of production. The birds on the high energy diet produced a significant higher egg mass per hen during the first period of production (week 23 - 35). Hatchability was reduced (P < 0,05) by the higher energy intake for the total period of production and this effect was very significant (P < 0,01) during the final period of production. Similar to hen day production, the higher energy had a significant (P < 0,05) negative effect on the amount of chicks produced. The well-known correlation between egg weight and chick weight was confirmed with the regression equation: Chick weight = 10,5 + 1,22 x Egg weight. Both energy and protein had a significant (P < 0,01) positive effect on chick weight. The feed conversion was lower at increasing levels of amino acid intake (P < 0,01). Higher energy intake significantly (P < 0,05) increased hen weight and protein had a very significant effect during the first period of production (P < 0,01). The isotope dilution technique (tritiated water) was used to estimate the body composition of the breeders. This was done at 5 different periods (week 27, 35, 43, 52 and 61) of the production period to establish changes in requirements over time. Significant correlation were found between carcass moisture and waterspace (R2 = 0,76); fat % and carcass moisture (R2 = 0,78); protein % and waterspace (R2 = 0,35) and fat % and waterspace (R2 = 0,46). The regression equations obtained from these correlation were employed to determine excess energy and lysine consumed at different ages. Energy requirements were calculated according to the effective energy (EE) system and the conventional ME system. According to effective energy the lower energy intake was not sufficient and the maximum requirement was calculated to be 1942 kj EE/day. The metabolizable energy calculations indicated sufficient intakes at every treatment with the maximum requirement 1746 kj ME/day. The lysine requirement was found to be in excess of 1050 mg lysine per day. The recommendation for daily lysine intake is 1200 mg/day and the energy intake of breeders should be 1900 to 2000 kj ME/day from week 23 to 35 and can be reduced to 1800 kj ME/day in the final period of production. / AFRIKAANSE OPSOMMING: Om die effek van verskillende vlakke energie en proteïen op produksie en liggaamsamestelling te ondersoek is 'n trop van 500 Hybro braaikuiken teelouers gebruik. Die daaglikse lisien inname van die henne was onderskeidelik 900, 1050, 1200 en 1350 mg, wat elk by 'n daaglikse energie inname van 1800 en 2000 kJ ME verskaf is, in 'n 4 x 2 faktoriale ontwerp. Alle aminosure is in 'n konstante verhouding met die verwysings aminosuur lisien in die rantsoen ingesluit. Om te evalueer of daar veranderinge oor 'n tydperk plaasvind weens die verskillende behandelings is die produksie periode in drie periodes van 13 weke elk verdeel (week 23 - 35; week 36 - 48 en week 49 - 61). Die produksie standaarde wat gemeet is, is hen dag produksie, eiergewig (g/eier), eiermassa (g/dag), vrugbaarheid, uitbroeibaarheid, kuikens/hen/week, voeromset en dagoud kuikenmassa. Hen dag produksie was betekenisvol (P < 0,05) laer by die hoër energie innames in die laaste periode van 49 tot 61 weke. Energie en proteïen het eiergewig betekenisvol (P < 0,01) verhoog. Die effek van hoër vlakke proteïen was konstant in alle produksie periodes. Die daaglikse eiermassa (g/dag) het ook saam met stygende vlakke proteïen verhoog en hierdie effek was vir die totale periode van produksie. Energie het die eiermassa in die eerste periode van produksie (week 23 - 35) verhoog. Uitbroeibaarheid is verlaag (P < 0,05) vir die totale periode van produksie deur die hoër energie inname en die effek was selfs groter (P < 0,01) in die finale periode van produksie. In ooreenstemming met die hen dag produksie is die aantal kuikens geproduseer negatief beïnvloed deur die hoër energie inname (P < 0,05). Die korrelasie wat bestaan tussen eiermassa en kuikenmassa is bevestig deur die regressie: Kuikenmassa = 10,5 + 1,22 x Eiermassa. Energie en proteïen het kuikenmassa betekenisvol (P < 0,01) verhoog. Voeromset was laer by stygende vlakke van proteïen inname (P < 0,01). Die hoër energie inname het henmassa ook betekenisvol (P < 0,05) verhoog en proteïen het dieselfde effek slegs in die eerste periode van produksie gehad (P < 0,01). Die liggaamsamestelling van teelhenne is bepaal met behulp van die isotoop verdunnings tegniek (tritium water). Dit is bepaal op 5 verskillende stadiums in die produksie periode (week 27, 35, 43, 52 en 61) om die moontlike verandering in behoeftes oor tyd vas te stel. Betekenisvolle korrelasies is gevind tussen karkasvog en die waterspasie (RZ= 0,76); vet % en karkasvog (R2 = 0,78); proteïen % en waterspasie (R2 = 0,35) en vet % en waterspasie (R2 = 0,46). Die regressie vergelykings van hierdie korrelasies is gebruik om die hoevelheid surplus energie en lisien ingeneem te bepaal. Die" effective energy" sisteem en die konvensionele ME sisteem is gebruik in die bepaling van energie behoeftes. Volgens die " effective energy" was die energie inname nie voldoende by die laer energie innames nie en die maksimum behoefte is bereken as 1942 kJ EE/dag. Die maksimum energie behoefte volgens metaboliseerbare energie is bereken as 1746 kj ME/dag. Die lisien behoefte moet hoër as 1050 mg/dag wees. Die aanbeveling van die daaglikse lisien inname is 1200 mg/dag en die energie inname moet 1900 tot 2000 kj/dag wees tot 35 weke produksie en kan daarna verlaag word na 1800 kJ ME/dag.