Five experiments were conducted to evaluate the potential use of plasma urea N (PUN) concentrations as a rapid response criterion to determine amino acid requirements. A preliminary experiment (Exp. 1) indicated that a 3-d feeding time was required to re-equilibrate PUN concentrations after a change in the dietary concentration of lysine. In Exp. 2, 3, and 4, PUN was used to estimate the lysine requirement of growing pigs at different specific BW. Thirty individually penned crossbred pigs weighing 32 and 44 kg in Exp. 2 and 3, respectively, were assigned to five dietary treatments (.60, .70, .80, .90, and 1.00% lysine) for 5 d. The PUN decreased quadratically (P < .05) to increasing dietary lysine. A two-slope, broken-line regression model estimated the requirement at .85% in Exp. 2 and at .76% in Exp. 3. In Exp. 4, 60 crossbred pigs (30 barrows and 30 gilts) weighing 70 kg were assigned to five dietary lysine concentrations: .50, .60, .70, .80, and .90% for 4 d. Increasing lysine caused PUN to decrease quadratically (P < .01). The estimated requirements were different (P < .05) between sexes: .69% for barrows and .75% for gilts. In Exp. 5, the validity of using PUN as a rapid response criterion was verified by comparing the estimated lysine requirement based on PUN with the requirement determined in a 7-d N balance. Twenty crossbred barrows averaging 19 kg were used. Dietary lysine concentrations were .60, .75, .90, 1.05, and 1.20%. A quadratic response was observed in PUN (P < .05) and N retention (NR) (P < .01) with increasing lysine. The estimated lysine concentrations that maximized rates of NR and minimized PUN (1.03 vs. 1.05) were not different (P > .10). Therefore, PUN concentrations can be used in short-term trials to accurately estimate the dietary lysine required to maximize total N utilization in pigs at a specific BW. In addition, the two-slope broken-line regression model had the highest R2 and the lowest mean square error compared with three other models as means for estimating lysine requirement from PUN concentrations.

No abstract

No abstract

The objectives of this study were 1) to investigate the relationship between plasma urea N concentrations (PUN) and lean tissue growth and 2) to compare the value of different variables, related to lean growth and renal function, to correct the relationship between dietary lysine concentration and PUN response for variation not related to amino acid adequacy. Forty-eight gilts (64.8 kg BW) were individually penned (blocks based on initial BW) for 50 d: a 10-d adjustment, a 35-d pretreatment, and a 5-d treatment period. During the pretreatment period, ADFI, urine specific gravity (SG), serum creatinine (SC), PUN, and daily fat-free carcass lean (DFFCL), empty body protein (DEBP), total carcass fat (DCF), and empty body lipid (DEBLI) depositions were measured. Partial correlation coefficients (ADFI effect removed) indicated a strong and inverse relationship between PUN and lean growth (DFFCL and DEBP) (r = -.88 and -.91, respectively, P < .01) and a positive relationship between PUN and fat deposition (DCF and DEBLI) (r = .66 and .54; respectively, P < .22). Treatments consisted of six dietary lysine concentrations (.475, .550, .625, .700, .775, and .850%). Initial and final BW in the treatment period were 103.3 and 107.7 kg, respectively. Pretreatment PUN (PUNO) was the pretreatment variable with the greatest R2 and the smallest MSE when used in the model describing the response of PUN (PUN1) to dietary lysine. The estimated lysine requirements from the PUN1 response corrected with either PUN0 or with the combination of PUN0, ADFI, DFFCL, DCF, SG, and SC were not (P > .05) different (.656 vs > 678%, respectively). We conclude that 1) PUN concentrations have a potential value as an indicator of the efficiency of lean tissue growth and 2) pretreatment PUN is a useful variable to correct treatment PUN for variation not related to amino acid adequacy.

Pregnant sow nutrition has potential effects on the muscle fiber development of progeny in utero. A total of 199 Landrace x Large White sows from parities 0 to 6 and their offspring were used to evaluate the effects of increasing the feeding amount during midpregnancy on the muscle tissue, growth performance, and meat quality of the progeny. The experiment was divided into 2 study replicates, and in each replicate, sows were assigned to 1 of the 2 treatments: 1) sows in the control group (C sows) were fed 2.5 to 3.0 kg/d (feed: 12.1 MJ of ME/kg and 0.62% lysine) throughout gestation; and 2) sows in the high group (H sows) received an extra feed allowance of 1.5 kg/d for gilts and 2.0 kg/d for multiparous sows above the C amount from d 45 to 85 of gestation (period of secondary muscle fiber formation). Sow backfat was recorded on d 40 and 85 of gestation. Sow performance (litter size and piglet BW) at farrowing and on d 18 of lactation was measured. At weaning, pigs were divided into 5 BW groups/treatment, and progeny growth performance was measured during the nursery (n = 958) and the growing-finishing (n = 636) periods. At slaughter, carcass and meat quality traits (lean content, main cut weight, pH, Minolta color, and drip loss) were recorded from the second lightest group at weaning (BW group 4; n = 90), and samples from the longissimus thoracis muscle were taken to study muscle fiber characteristics (n = 70). The extra nutrition from d 45 to 85 of gestation did not lead to differences in litter size or piglet BW at farrowing and on d 18 of lactation. Pigs born to H mothers had fewer muscle fibers and fewer estimated primary and secondary fibers than did pigs born to C mothers (P < 0.05). However, postnatal growth performance was not consistently affected by the maternal treatment. The smaller number of muscle fibers found in the H group of pigs was associated with fewer type IIB fibers (P < 0.05) with greater cross-sectional areas (P < 0.10), which might be related to the significantly greater meat pH at 24 h postmortem and the smaller L* (lightness) values recorded in the H group of pigs. Results from the present study confirm the existence of effects of maternal nutrition on fetal development, at least in terms of muscle tissue development and meat quality, although with no beneficial effects were found for the postnatal growth performance of the progeny.