Effects of crude protein content, protein degradability and energy concentration of the diet on growth and carcass characteristics of market lambs fed high concentrate diets

Abstract

y=a+b(I-e-c(t'tl'l fort>L, (1) where a is the soluble fraction (Vo), b is the slowly digestible fraction (7o), c is the rate of disappearance (7o h-1), r is the time of incubation (h), L is lag time (h).Protein solubility was estimated as the soluble fraction, while effective rumen degradability was estimated using the model proposed by Merlens (1917): Blood samples were obtained via jugular venipuncture from male lambs approximately 3 wk from the start of the experiment on 13 June and prior to slaughter. Samples were preserved at -20"C and later analyzed for PUN (Technicon 1977 ribs. Probe measurements were taken on the left side of the unsplit carcass 2.5 cm from the carcass midline for rib-eye meisurements and 11 cm from the midline for TD' Carcasses were chilled for 24h at 1"C. The cold carcasses were sectioned with a knife between the l2th and 13th rib while hanging, exposing the entire right and left rib eye (m' longissimus thoracis). Average fat depth was determined at three locations along the rib-eye by using a ruler' Marbling was determined by subjective ranking based on a scale of 1-9, with 1 corresponding to extreme marbling and 9 to no marbling. Muscle (longissimus thoracis) colour was assessed using a reflectance meter (Minolta Chroma Meter II, Minolta Camera Co., NJ). Kidney and pelvic fat was removed from each carcass and weighed. Chemical AnalYsisFeces and feed were dried at 55"C and then ground to pass a l-mm screen for determination of nutrient content' Dry matter content was determined by drying at 135oC to a constant weight. Gross energy was determined by bomb calorimetry (Parr Instrument Corp., Moline, IL). Organic matter was determined by ashing samples in a muffle furnace at 550'C; CP content was determined by micro-

Performance of Santa Ines lambs fed diets of variable crude protein levels

“…However, better feed conversion ratios were observed when compared to results cited by Pérez et al (1998), who found FC values of 6.26 kg DM kg -1 gain for Santa Ines lambs and 6.05 kg DM kg -1 gain for Bergamasca lambs fed diets Beauchemin et al (1995) and Haddad et al (2001), also did not observed effects on feed conversion of lambs fed diets with different protein levels, with mean values of 5.8; 3.7 and 4.5 kg DM kg -1 gain, respectively. As expected, crude protein intake (Table 4) increased as diet protein level was higher; however, this greater intake did not elicit higher weight gain (Table 2).…”

“…Therefore, urea concentration in blood reflects the ingestion of dietary protein (Thomas et al, 1988). Bunting et al (1987) verified that plasma urea N percentage derived from rumen ammonia absorption was greater for lambs fed diets containing 15.4% CP, as compared to lambs fed 8.7% CP (16.5 and 6.1%, respectively). Beauchemin et al (1995) also found that increasing CP proportion (from 15 to 18%), in highly energetic diets, raised PUN concentrations from 12.9 to 18.6 mg dL -1 ; this effect remained until the end of the experiment.…”

“…Beauchemin et al (1995), studying diets with 15 and 18% CP, in Finn and Romanov lambs, also did not observed defferences between treatments, and suggested that effects of diets on performance were more related to energy concentration than to protein source or content in the diet.…”

“…The daily DM intake of the lambs (Table 3) , and is in agreement with the intake found by Morais et al (1999) and Susin et al (2000) for Santa Ines lambs fed diets containing 20% sugarcane bagasse and 80% concentrate (1.24 and 1.0 kg DM animal -1 day -1 , respectively). Some studies did not report diet CP concentration effects on DM intake (Beauchemin et al, 1995;Zundt et al, 2002). Manso et al (1998b) verified an average DM intake of 77.5 g kg -1 LW 0.75 for lambs fed diets with a high proportion of concentrate containing 14 or 26% CP.…”

Teores de proteína bruta em dietas com alta proporção de concentrado para cordeiros confinados.

“…O consumo e a digestibilidade aparente do N e PB foram maiores (P<0,05) para as dietas com 16, 18 e 20% PB em relação às dietas com 12 e 14% PB. Vários trabalhos têm verificado aumento na digestibilidade do N com o aumento do teor de N da dieta (Sultan & Loerch, 1992;Beauchmin et al, 1995;Lallo, 1996;Manso et al, 1998b;Haddad et al, 2001e Zundt et al, 2001c. Owens & Zinn (1988) verificaram que a regressão da digestibilidade de N contra a ingestão de N produz uma linha reta ao longo de uma grande variedade de dietas, de modo a concluir que a digestibilidade aparente de N varia com o teor de N da dieta.…”