Short communication: Performance of Holstein calves fed high-solid milk with or without nucleotide.

Our initial hypothesis was that the exogenous supply of nucleotides to neonatal calves would improve the development and functionality of gastrointestinal tissue, thereby enhancing their capacity to efficiently digest and utilize the nutrients in high-solids milk. Twenty 3-d-old male Holstein calves (37.9 ± 2.24 kg of body weight) were distributed randomly to 1 of 2 treatments (1 calf per pen; 10 pens per treatment) without or with added nucleotides to their daily milk. Dry milk powder was added to pasteurized milk and offered as 4 L/d from d 3 to 15, 6 L/d from d 16 to 49 (at 0900 and 1600 h), and 2 L/d in morning feeding from d 50 to 55. High-solids milk (fat = 4.47%, protein = 4.64%, lactose = 8.13%, and total solids = 17.7%) was made through the addition of milk powder into whole milk and supplemented without or with 2 g/d of a commercially available nucleotide product, and then fed until weaning. Nucleotide supplementation had no effect on preweaning growth rate, but tended to increase postweaning daily weight gain (d 56-75). Unexpectedly, nucleotide supplementation tended to increase fecal score within the 10 d of calf life; thereafter (until weaning), no difference was detected in fecal consistency. Nucleotide supplementation tended to increase and increased pre- and postweaning dry matter intake, respectively. Efficiency of feed utilization (kilogram of weight gain per kilogram of dry matter intake) was not influenced with treatment. The net gain (d 1-70) of withers height and hip height tended to be greater in nucleotide-fed calves. Overall, addition of nucleotides to the high-solids milk had marginal effects on preweaning performance and tended to increase fecal scores (looser feces) in the initial phase of life; however, it increased starter feed intake and growth rate after weaning. A longer-feeding experiment is recommended to elucidate the potential effects of nucleotide supplementation in high-solids milk on calf performance.

Effects of heat stress on metabolism, digestibility, and rumen epithelial characteristics in growing Holstein calves.

To distinguish between the direct effects of heat stress (HS) and reduced DMI on metabolic and physiological variables, morphometry, and gene expression of transporters involving in ruminal VFA absorption, 16 Holstein bull calves (178.1 ± 7.55 kg of BW) were used in a randomized complete design using 2 experimental periods. In period 1 (P1), all animals were housed in thermoneutral (TN) conditions (20.7 ± 3.0°C and a temperature-humidity index [THI] of 65.2 ± 3.1) and fed ad libitum for 8 d. In period 2 (P2; 9 d), half of the calves ( = 8) were subjected to HS condition (29.9 to 41.0°C and a THI ≥ 85 for 8 h/d) and the other half ( = 8) were maintained in TN conditions but were pair fed (pair-fed thermoneutral [PFTN]) to the HS calves. Heat stress decreased DMI (20%; < 0.01) and, by design, PFTN calves had similar reduced intakes. During P1, ADG was similar between groups (1.7 kg/d), but ADG was reduced similarly for both groups (0.14 kg/d) during P2 ( < 0.01). Compared with P1, HS calves had decreased plasma glucose levels (12.5%; < 0.01) in P2. Basal insulin levels increased in P2 for HS calves (71%; < 0.03), but there was no difference between periods for PFTN calves. Circulating NEFA concentrations did not differ between periods in the HS calves, but PFTN animals had increased basal NEFA levels (100%; < 0.01). Compared with P1, HS calves had increased blood urea nitrogen concentration in P2 ( < 0.01) but blood urea nitrogen did not differ between periods in the PFTN calves. Heat stress had no measurable effect on nutrient digestibility. Rumen papillae height increased (51%; < 0.04) in HS calves whereas papillae top width decreased (40%; < 0.03), but there was no difference between treatments for other morphometric parameters. Gene expression of VFA transporters in rumen epithelium was not affected by thermal treatments. These results confirmed that short-term HS in the current study had no effect on diet digestibility, rumen morphology, or VFA transporters genes. Therefore, HS-induced decrease in DMI is in large part responsible for gross changes in BW in growing calves (albeit tissue composition of growth is not unknown).

The effect of cyclical and severe heat stress on growth performance and metabolism in Afshari lambs.

The extent to which reduced feed intake contributes to decreased growth during heat stress (HS) in the ovine model is not clear. To evaluate the impact of decreased DMI on performance, we conducted an experiment on growing lambs experiencing a cyclical but extensive heat load. Sixteen intact male Afshari lambs (40.1 ± 1.9 kg) were used in a completely randomized design in 2 periods. In period 1, all 16 lambs were housed in thermal neutral (TN) conditions (22.2 ± 3.1°C and a temperature-humidity index [THI] of 67.9 ± 3.2) and fed at libitum for 8 d. In period 2 (P2), which lasted 9 d, 8 lambs were subjected to a cyclical HS condition (33.0 to 45.0°C and a THI of more than 80 at least for 24 h/d and more than 90 for 8 h/d). The other 8 lambs were maintained in TN conditions but pair-fed (pair-fed thermal neutral [PFTN]) to the HS lambs. During each period, DMI and water intake were measured daily. Respiration rate, rectal temperature, and skin temperature at the shoulder, rump, and front and rear leg were recorded at 0700 and 1400 h daily. Dry matte intake declined (17.5%; P < 0.01) in HS lambs and, by design, the temporal pattern and magnitude of reduced feed intake was similar in the PFTN controls. Water intake increased (19%; P < 0.05) during P2 in HS but not in the PFTN controls. Heat stress increased the 0700 and 1400 h skin temperature at the shoulder (5 and 9.2%), rump (6.2 and 10.3%), rear (6 and 9.2%), and front leg (6.5 and 9.8%) and respiratory rates (84 and 163% [P < 0.01]at 0700 and 1400 h, respectfully), but only the 1400 h rectal temperature was increased (P < 0.01; 0.65°C) in HS lambs. Neither environment nor period affected blood urea nitrogen and glucose concentrations. However, circulating NEFA and insulin were increased and declined (P < 0.01) in PFTN lambs, respectively, but neither variable was altered in the HS lambs. Growth was reduced in P2 for lambs in both treatments, but despite being on a similar reduced plane of nutrition, the HS lambs' ADG was more than 2-fold greater than the PFTN controls. These results indicate that HS markedly alters the energetics of weight gain during growth and that the effects of HS are dependent on the severity of the heat load.

The effect of cyclical and mild heat stress on productivity and metabolism in Afshari lambs.

To investigate the effect of heat stress (HS) on production and metabolism of Afshari sheep, 32 intact male lambs (33.2 ± 4.5 kg) were used in a completely randomized design using 2 experimental periods. In period 1 all 32 lambs were housed in thermal neutral (TN) conditions (25.6 ± 2.6°C and a temperature-humidity index [THI] of 72.0 ± 2.6) and fed ad libitum for 8 d. In period 2 (P2; 9 d), 16 lambs were subjected to cyclical HS (29.0 to 43.0°C and a THI ≥80 for 24 h/d) and the other 16 lambs were maintained in TN conditions but pair fed (pair-fed thermal neutral [PFTN]) to the HS lambs. During each period DMI and water intake were measured daily. Respiration rate, rectal temperature, and skin temperature at the shoulder, rump, and front and rear leg were recorded at 0700 and 1400 h daily. Water intake increased (P < 0.05) during P2 in both HS and TN lambs (88 and 35%, respectively). Heat stress increased the 0700 and 1400 h surface temperature at the shoulder (3.0 and 10.6%), rump (2.7 and 12.7%), rear leg (3.1 and 13%), and front leg (3.0 and 13%) and respiratory rates (72 and 124%; P < 0.01, respectively, for 0700 and 1400 h) but only the 1400 h rectal temperature was increased (P < 0.01; 0.54°C) in HS lambs. Plasma glucose concentration decreased in P2 (P < 0.01) in both the HS and PFTN lambs. Basal insulin concentrations decreased in PFTN controls but increased in HS lambs (environment × period interaction; P < 0.05). Blood urea nitrogen concentration was not affected by environment or period, but NEFA levels were slightly elevated (P < 0.01) in both PFTN and HS lambs during P2. Interestingly, HS did not affect DMI, but ADG was reduced (36%; P < 0.01) compared to the PFTN lambs. These results indicate that the direct effects of heat (not mediated by reduced DMI) are partially responsible for reduced growth in heat-stressed lambs.

Quantitative genetics of Taura syndrome resistance in Pacific white shrimp (Penaeus vannamei): a cure model approach.

BACKGROUND: In aquaculture breeding, resistance against infectious diseases is commonly assessed as time until death under exposure to a pathogen. For some diseases, a fraction of the individuals may appear as "cured" (non-susceptible), and the resulting survival time may thus be a result of two confounded underlying traits, i.e., endurance (individual hazard) and susceptibility (whether at risk or not), which may be accounted for by fitting a cure survival model. We applied a cure model to survival data of Pacific white shrimp (Penaeus vannamei) challenged with the Taura syndrome virus, which is one of the major pathogens of Panaeid shrimp species. METHODS: In total, 15,261 individuals of 513 full-sib families from three generations were challenge-tested in 21 separate tests (tanks). All challenge-tests were run until mortality naturally ceased. Time-until-event data were analyzed with a mixed cure survival model using Gibbs sampling, treating susceptibility and endurance as separate genetic traits. RESULTS: Overall mortality at the end of test was 28%, while 38% of the population was considered susceptible to the disease. The estimated underlying heritability was high for susceptibility (0.41 ± 0.07), but low for endurance (0.07 ± 0.03). Furthermore, endurance and susceptibility were distinct genetic traits (rg = 0.22 ± 0.25). Estimated breeding values for endurance and susceptibility were only moderately correlated (0.50), while estimated breeding values from classical models for analysis of challenge-test survival (ignoring the cured fraction) were closely correlated with estimated breeding values for susceptibility, but less correlated with estimated breeding values for endurance. CONCLUSIONS: For Taura syndrome resistance, endurance and susceptibility are apparently distinct genetic traits. However, genetic evaluation of susceptibility based on the cure model showed clear associations with standard genetic evaluations that ignore the cure fraction for these data. Using the current testing design, genetic variation in observed survival time and absolute survival at the end of test were most likely dominated by genetic variation in susceptibility. If the aim is to reduce susceptibility, earlier termination of the challenge-test or back-truncation of the follow-up period should be avoided, as this may shift focus of selection towards endurance rather than susceptibility.

Combined detection and introgression of QTL in outbred populations.

BACKGROUND: Detecting a QTL is only the first step in genetic improvement programs. When a QTL with desirable characteristics is found, e.g. in a wild or unimproved population, it may be interesting to introgress the detected QTL into the commercial population. One approach to shorten the time needed for introgression is to combine both QTL identification and introgression, into a single step. This combines the strengths of fine mapping and backcrossing and paves the way for introgression of desirable but unknown QTL into recipient animal and plant lines. METHODS: The method consisting in combining QTL mapping and gene introgression has been extended from inbred to outbred populations in which QTL allele frequencies vary both in recipient and donor lines in different scenarios and for which polygenic effects are included in order to model background genes. The effectiveness of the combined QTL detection and introgression procedure was evaluated by simulation through four backcross generations. RESULTS: The allele substitution effect is underestimated when the favourable QTL allele is not fixed in the donor line. This underestimation is proportional to the frequency differences of the favourable QTL allele between the lines. In most scenarios, the estimates of the QTL location are unbiased and accurate. The retained donor chromosome segment and linkage drag are similar to expected values from other published studies. CONCLUSIONS: In general, our results show that it is possible to combine QTL detection and introgression even in outbred species. Separating QTL mapping and introgression processes is often thought to be longer and more costly. However, using a combined process saves at least one generation. With respect to the linkage drag and obligatory drag, the results of the combined detection and introgression scheme are very similar to those of traditional introgression schemes.

Introgression of a major QTL from an inferior into a superior population using genomic selection.

BACKGROUND: Selection schemes aiming at introgressing genetic material from a donor into a recipient line may be performed by backcross-breeding programs combined with selection to preserve the favourable characteristics of the donor population. This stochastic simulation study investigated whether genomic selection can be effective in preserving a major quantitative trait locus (QTL) allele from a donor line during the backcrossing phase. METHODS: In a simulation study, two fish populations were generated: a recipient line selected for a production trait and a donor line characterized by an enhanced level of disease resistance. Both traits were polygenic, but one major QTL affecting disease resistance was segregating only within the donor line. Backcrossing was combined with three types of selection (for total merit index) among the crossbred individuals: classical selection, genomic selection using genome-wide dense marker maps, and gene-assisted genomic selection. It was assumed that production could be observed directly on the selection candidates, while disease resistance had to be inferred from tested sibs of the selection candidates. RESULTS: Classical selection was inefficient in preserving the target QTL through the backcrossing phase. In contrast, genomic selection (without specific knowledge of the target QTL) was usually effective in preserving the target QTL, and had higher genetic response to selection, especially for disease resistance. Compared with pure genomic selection, gene-assisted selection had an advantage with respect to disease resistance (28-40% increase in genetic gain) and acted as an extra precaution against loss of the target QTL. However, for total merit index the advantage of gene-assisted genomic selection over genomic selection was lower (4-5% increase in genetic gain). CONCLUSION: Substantial differences between introgression programs using classical and genomic selection were observed, and the former was generally inferior with respect to both genetic gain and the ability to preserve the target QTL. Combining genomic selection with gene-assisted selection for the target QTL acted as an extra precaution against loss of the target QTL and gave additional genetic gain for disease resistance. However, the effect on total merit index was limited.

Increasing prepartum dietary crude protein using poultry by-product meal dose not influence performance of multiparous Holstein dairy cows.

The aim of this study was to compare the effects of two levels of Crude Protein (CP) using Poultry by-Product Meal (PBPM) fed during late gestation on the performance, blood metabolites and colostrum composition of Holstein cows. Twenty multiparous cows 26 +/- 6 days before expected calving were assigned randomly to two treatments containing 1) 140 g kg(-1) DM CP (34 g kg(-1) DM PBPM) 2) 160 g kg(-1) DM CP (75 g kg(-1) DM PBPM). The cow's BCS was 3.56 +/- 0.5 on average, at the beginning of the trial. Yields of milk, protein, lactose and fat were not affected by prepartum dietary CP level. Colostrum composition (fat, CP and total solids percents), blood metabolites (Ca, glucose, total protein, albumin, globulin, urea N and cholesterol) and metabolic diseases incidence were not influenced by prepartum dietary CP level. There was no significant difference between treatments in body weight and BCS changes. As expected, blood urea N before calving was higher in the cows fed 160 g kg(-1) DM CP diets (p < 0.002). Serum cholesterol during prepartum (p < 0.03) and postpartum (p < 0.01) periods was significantly lower in 160 g kg(-1) DM CP treatment. In general, although postpartum glucose level increased in cows which received 160 g kg(-1) DM CP in the diet, it seems that there is no other obvious advantages over feeding the 140 g kg(-1) DM CP diet. So feeding this level of CP diet to close up cows is recommended.