Effects of pre-weaning concentrate feeding on calf performance, carcass and meat quality of autumn-born bull calves weaned at 90 or 150 days of age

A study was conducted to evaluate the effect of pre-weaning concentrate feeding in early-weaned (EW, day 90) or traditionally weaned (TW, day 150) autumn-born beef calves on growth, feed intake and feed efficiency, and carcass and meat quality. Twenty-eight male calves were either EW or TW, and offered a starter concentrate (S) or no additional feed (NS) during the pre-weaning period. Therefore, four management strategies were tested: EWS, EWNS, TWS and TWNS. Growth patterns were affected by management strategy. From day 90 to 150, TWNS calves presented a substantially lower average daily gain (ADG) than their counterparts, which had similar performance. During the finishing phase (from day 150 to slaughter at 450 kg live weight), EWS calves had the lowest ADG. Daily feed intake or efficiency in the finishing phase was unaffected by previous management. Serum IGF-I concentrations at day 90 and slaughter did not differ with management strategy, but early weaning and pre-weaning concentrate feeding increased IGF-I concentrations at day 150. Circulating leptin concentrations were unaffected by age at weaning and pre-weaning concentrate feeding, except for leptin concentrations at slaughter, which were higher in S calves than in NS calves. Total concentrate intake from birth to slaughter and the concomitant feed costs were higher for EWS and EWNS calves than for TWNS and TWS ones. However, cow feed costs were lower for cows whose calves had been early weaned. Concerning carcass quality, early weaning improved dressing percentage and increased fatness score, and particularly TWNS calves presented a poorer conformation. Meat quality was not affected by management strategy. Considering the economic performance, TWS, EWNS and EWS strategies yielded a similar economic margin, whereas TWNS would be the least advisable strategy when calves are fattened in the farm until slaughter.     

Autophagy during beef aging

The conversion of muscle into meat is a complex process of major concern for meat scientists due to its influence on the final meat quality. The aim of this study was to investigate the occurrence of autophagic processes in the conversion of muscle into meat. Our findings demonstrated, for the first time, the occurrence of autophagic processes in the muscle tissue at early postmortem period (2 h to 24 h) in both beef breeds studied (Asturiana de los Valles and Asturiana de la Montaña) showing significant time-scale differences between breeds, which could indicate a role of this process in meat maturation. These breeds have different physiological features: while Asturiana de los Valles is a meat-specialized breed showing high growth rate, an elevated proportion of white fibers in the muscle and low intramuscular fat level, Asturiana de la Montaña is a small- to medium-sized rustic breed adapted to less-favored areas, showing more red fibers in the muscle and a high intramuscular fat content.     

Weaning distress in dairy calves: Effects of alternative weaning procedures

The aims of this study were to describe the behavioural responses to weaning from milk in dairy calves, and to compare responses when calves were either weaned abruptly (removal of the milk-feeding system; n = 8 calves) or by substituting warm water for milk in the milk-feeding apparatus for the first 2 days after weaning (n = 8 calves). Calves provided water through the milk-feeding system after weaning seemed to substitute one liquid for the other; calves consumed approximately the same quantity of warm water after weaning (8 kg/day) as they had consumed milk before weaning (9 kg/day). All calves vocalized at weaning, but abruptly weaned calves vocalized at more than three times the rate of calves provided water through the milk-feeding system. On the third day after weaning, when neither treatment group had access to the milk-feeding system, the call rate was similar in the two treatment groups. The abruptly weaned calves were also more active at weaning, as indicated by an increased number of standing bouts compared to calves with continued access to the milk-feeding apparatus. The reduced response to weaning by the calves with continued access to the feeding routine may be due to the gut fill associated with the water intake or to other rewarding properties of the system (e.g. allowing calves to suck on a teat). In conclusion, dairy calves show a strong behavioural response to weaning, but providing calves continued access to the milk-feeding apparatus for 2 days after weaning reduces this response.     

Reducing the incidence of short estrous cycles in beef cows with norgestomet

Twenty-nine anestrous cows suckling calves 27 to 67 days old were allotted to 3 treatment groups according to calving date. Calves were weaned from all cows; 9 cows received no further treatment, while 10 were implanted with 6 mg of norgestomet 9 days before calves were weaned and 10 were implanted when calves were weaned. All implants were removed after 9 days. Twenty-two cows exhibited estrus within 10 days after treatment, and all exhibited estrus within 25 days. In the cows exhibiting estrus in 10 days, norgestomet reduced the incidence of 8 to 12-day cycles from 83.3 percent in the control group to 30 percent when implanted before weaning and to zero when implanted at weaning. Conception rates at first service were increased from zero for cows which were not implanted to 33.3 and 80 percent for those implanted before and at weaning, respectively. These data demonstrate that the presence of a progestogen before the first postpartum estrus increases conception rates and reduces the percentage of previously anestrous cows exhibiting short estrous cycles after their calves are weaned.     

Minimizing cows’ stress when calves were early weaned using the two-step method with nose flaps

Early weaning may be used in beef cattle production to improve reproduction rates in range conditions. However, weaning causes a stress response in cows, which may be especially strong in early weaning management, as the bond between the cow and the calf is still strong. We hypothesized that weaning calves in two steps, with the aid of anti-sucking devices (nose flaps) would reduce the behavioural stress response in the cows separated from their calves 2 months after parturition. We compared the behaviour frequency and weight change in cows that were weaned abruptly, by separation of the calf on day 0 of the study, or in two steps, consisting of the use of anti-sucking nose flaps for 5 days before permanent separation; a third group was not weaned to serve as control. Thirty-six crossbred multiparous Aberdeen Angus×Hereford cows and their calves (n=12/treatment) were managed in three paddocks with similar pasture availability, with four dyads from each treatment per paddock. Cows’ behaviour was observed by direct visual instantaneous sampling, at 10 min intervals from days −3 to 11. Weaning the calves in two steps clearly attenuated the behavioural stress response observed in abruptly weaned cows, which included reductions in grazing and lying, and increases in pacing, walking and vocalizing. Our results corroborate those previously shown for cows nursing older calves, and indicate that step weaning can reduce the behavioural stress response of cows at weaning, even when the calf is weaned shortly after birth, when the bond between the cow and calf is still very strong.     

Effects of Feeding Selenium-Enriched Alfalfa Hay on Immunity and Health of Weaned Beef Calves

Previously, we reported that feeding selenium (Se)-enriched forage improves antibody titers in mature beef cows, and whole-blood Se concentrations and growth rates in weaned beef calves. Our current objective was to test whether beef calves fed Se-enriched alfalfa hay during the transition period between weaning and movement to a feedlot also have improved immune responses and slaughter weights. Recently weaned beef calves (n?=?60) were fed an alfalfa-hay-based diet for 7 weeks, which was harvested from fields fertilized with sodium selenate at 0, 22.5, 45.0, or 89.9 g Se/ha. All calves were immunized with J-5 Escherichia coli bacterin. Serum was collected for antibody titers 2 weeks after the third immunization. Whole-blood neutrophils collected at 6 or 7 weeks were evaluated for total antioxidant potential, bacterial killing activity, and expression of genes associated with selenoproteins and innate immunity. Calves fed the highest versus the lowest level of Se-enriched alfalfa hay had higher antibody titers (P?=?0.02), thioredoxin reductase-2 mRNA levels (P?=?0.07), and a greater neutrophil total antioxidant potential (P?=?0.10), whereas mRNA levels of interleukin-8 receptor (P?=?0.02), l-selectin (P?=?0.07), and thioredoxin reductase-1 (P?=?0.07) were lower. In the feedlot, calves previously fed the highest-Se forage had lower mortality (P?=?0.04) and greater slaughter weights (P?=?0.02). Our results suggest that, in areas with low-forage Se concentrations, feeding beef calves Se-enriched alfalfa hay during the weaning transition period improves vaccination responses and subsequent growth and survival in the feedlot.     

Adipocyte cellularity in different adipose depots in bulls of seven Spanish breeds slaughtered at two body weights

The influence of body weight (BW) at slaughter and genotype on adipocyte size and number in the omental (OM), perirenal (PR), subcutaneous (SC) and intermuscular (IM) adipose tissues was studied in 168 bulls of Spain's local Asturiana, Avileña, Morucha, Parda Alpina, Pirenaica, Retinta, and Rubia Gallega cattle breeds. The young bulls were slaughtered at two BWs, 320 and 540 kg. The results obtained showed the higher amounts of lipids that accumulated between 320 and 540 kg BW (P < 0.001) to be ascribable primarily to adipose cell hypertrophy, i.e. larger adipocyte size, in the OM and PR depots (P < 0.001). In addition to hypertrophy, there was also an increase (P < 0.001) in the number of adipose cells, i.e. hyperplasia, in the SC and IM adipose depots. Significant differences were observed when comparing the different genotypes, with the Morucha, Retinta and Avileña breeds having the highest amount of adipose tissue and the largest adipocytes. The Asturiana and Rubia Gallega breeds had the lowest amount of adipose tissue and the smallest adipocytes. The Pirenaica and Parda Alpina breeds had intermediate values in between the two groups identified above. In short, the results were indicative of different lipid deposition patterns in the different breeds depending on the individual growth and maturation rates in each. Similar findings were made when comparing the different adipose tissue depots, with adipocyte hypertrophy being the main factor responsible for lipid accumulation in the OM and PR depots, as opposed to adipocyte hyperplasia in the SC and IM depots.     

Effect of roughage level in a total mixed ration on feed intake, ruminal fermentation patterns and chewing activity of early-weaned calves with ad libitum access to grass hay

In this study, two total mixed rations (TMR, based on dry ingredients) consisting (per kg dry matter (DM)) of 300 or 400 g finely chopped hay mixture of grass and alfalfa (H30 versus H40) were compared concerning their effects on dry matter intake (DMI), ruminal fermentation patterns and chewing activity of early-weaned (8 weeks milk-fed) calves. Ten ruminally cannulated male German Holstein calves were randomly assigned to two dietary treatments (n = 5) and observed from an age of 8–15 weeks. One group received the H30 (11.3 MJ metabolizable energy (ME)/kg DM) and the other the H40 (10.7 MJ ME/kg DM) TMR. All calves received grass hay (9.0 MJ ME/kg DM) separately. Water, TMR and hay were offered ad libitum twice daily (08:00 and 16:00 h). Rumen fluid was collected via cannula at an age of 9, 11, 13 and 15 weeks, twice weekly just prior to as well as 1, 3, 5 and 7 h after morning feeding. Chewing activity was recorded by a special head collar. As the calves aged DMI increased rapidly congruent with the recommended range for weaned calves. Because of the differing energy supply, calves receiving the H30 TMR were heavier than calves receiving the H40 TMR (139 kg versus 123 kg, P=0.007). During the trial ruminal pH of all calves were within the target range (6.2 ± 0.5), indicating physiological ruminal fermentation patterns. Daily mean ruminal pH was uninfluenced by treatment, however at an age of 13 and 15 weeks H30 showed a higher short chain fatty acid (SCFA) level than H40 (P=0.098; P=0.036). At an age of 15 weeks H30 showed a critical decrease in ruminal pH (3 h after feeding: 5.7) corresponding to a higher ruminal SCFA concentration (148.2 mmol/L, P=0.007). Chewing activity was well developed at an early age due to an increasing DMI after weaning. At an age of 15 weeks chewing activity (per day: 613–743 min total chewing; 358–418 min rumination) was similar to that of adult cows. In summary, feeding a dry TMR consisting per kg DM of 300–400 g hay to early-weaned calves can be recommended for a successful calf rearing up to an age of 15 weeks.     

Comparative effects of early weaning or once-daily suckling on occurrence of postpartum estrus in primiparous beef cows

We concurrently evaluated early weaning and once-daily suckling as options for shortening postpartum interval to estrus in primiparous cows calving in good body condition. Over 2 consecutive years, a total of 77 primiparous cows were assigned to 1 of 3 treatments: control (ad libitum suckling); once-daily suckling (for 30 d prior to start of breeding); or early weaning (calves weaned 30 d prior to start of breeding). All cows had a body condition score (BCS) of > or = 5 at parturition and were maintained in good condition throughout the breeding season. Cows were observed for estrus twice daily and blood samples for subsequent measurement of progesterone were collected at 48-h intervals. For data analysis, cows were divided into early- (> or = 85 d post partum) and late-calving (< 85 d post partum) groups at the onset of the breeding season. All calves were weighed at birth, at the onset of treatment, at weekly intervals until the start of the breeding season, and within 45 d of 205 d of age. Early weaning or once-daily suckling shortened the postpartum interval to first estrus of late-calving primiparous cows by 17 (P < 0.01) and 12 d (P < 0.08), respectively, compared with control group cows. However, among early-calving cows, neither early weaning nor once-daily suckling influenced the postpartum interval. Postpartum intervals of once-daily suckled cows and early-weaned cows were similar (P > 0.10).     

Physiological and behavioural responses of cows from two beef breeds submitted to different suckling strategies

This experiment was designed to study the effects of avoiding calf contact and genotype on the metabolic, behavioural and reproductive traits of beef cows during lactation. Fifty-two multiparous cows, 25 Parda de Montaña (PA) and 27 Pirenaica (PI), fed at maintenance were assigned from the day after calving to twice-daily nursing (2× 30-min sessions at 0800 and 1600 h) either with fence contact with their calves (partial contact, PC) or without visual, tactile and olfactory contact (non-contact, NC) between suckling periods. Blood samples were collected to analyse metabolites (triglycerides, cholesterol, non-esterified fatty acids (NEFA), β-hydroxybutyrate and urea) and progesterone at different intervals. Cow–calf behaviour was monitored on weeks 4, 9 and 15 of lactation. Cow activity at oestrus was recorded through collars. Cows from both treatments and breeds showed similar live-weight gains during the first three months post-partum (P > 0.10). Milk yield and calf gains were not affected by treatment (P > 0.10) but they were greater in PA than in PI (P < 0.05). Plasma triglycerides and urea in the cows were not affected either by calf contact, breed or week post-partum (P > 0.10). Plasma cholesterol increased from week 6 post-partum onwards in PA cows (P < 0.05) while this rise was delayed to week 7 of lactation in PI breed (P < 0.05). Plasma NEFA was greater in blood from PC–PA cows than in the rest of groups (P < 0.05), and these metabolites were greater on week 1 and lower on week 11 than in rest of samplings (P < 0.05). Plasma β-hydroxybutyrate was not affected by either calf contact or breed (P > 0.10), but it was greatest on weeks 1–3 than in the rest of lactation (P < 0.05). Cows with PC calves took less time to first contact after they entered the barn than their NC counterparts (P < 0.05). Dams from both contact treatments nursed their offspring and remained in close proximity for similar time within suckling periods (P > 0.10). PA cows devoted more time than PI ones to lick their young (P < 0.001). There were no differences throughout lactation in any of the studied maternal behaviours (P > 0.10). Calf contact and breed did not affect the interval to first post-partum ovulation or oestrus in these cows (P > 0.10). Under twice-daily nursing conditions, the limitation of visual, tactile and olfactory contact with calves did not trigger different maternal or reproductive traits in these breeds but only a slightly higher mobilisation of body fat substrates in Parda de Montaña compared to Pirenaica.     

Interactive response of the horn fly (Diptera: Muscidae) and selected breeds of beef cattle

Statistically significant differences were observed in the population density of the horn fly, Haematobia irritans irritans (L.), on different breeds of beef cattle. The European breed Chianina had a population density of horn flies generally less than or equal to 50% than that of the British cattle breeds (Angus, Hereford, Polled Hereford, and Red Poll) and another European breed (Charolais). Generally, no significant difference existed among numbers of horn flies on Hereford, Polled Hereford, and Red Poll cows in 1988 or among Angus, Hereford, Polled Hereford, and Red Poll cows in 1989. Factors other than color appeared to be involved in the selective process between the horn fly and its host. Population densities on two white European breeds (Charolais and Chianina) were significantly different on all weekly intervals except for 4 wk in both 1988 and 1989. No significant difference existed among Charolais and British breeds except during 4 wk in 1988 and 3 wk in 1989. When weaning weights of all calves were adjusted for the effects of age to 205 d, sex of calf, and age of dam, the indirect effect of the horn fly on weaning weight showed a significant linear regression. Each 100 flies per cow caused a reduction of 8.1 kg in calf weaning weight. Cows within each breed with low numbers of horn flies weaned significantly heavier calves than cows with higher numbers of horn flies.     

Performance and nursing behaviour of beef cows with different types of calf management

The aim of this experiment was to evaluate the effect of calf management during lactation on dam performance and nursing behaviour. Thirty-six multiparous beef cows (aged 7.5 ± 0.52 years) of Parda de Montaña breed (mean live-weight (LW) at calving 566 ± 9.3 kg) with a moderate body condition (mean 2.6 ± 0.02 on a 1 to 5 scale), were assigned to three nursing frequencies from the day after parturition: Once-daily restricted nursing during a 30 min period at 0800 h (RESTR1), twice-daily restricted nursing during two 30 min periods at 0800 and 1530 h (RESTR2) and ad libitum nursing (ADLIB). Cows were fed throughout the experiment 80 MJ/day of metabolizable energy. Cow–calf behaviour recordings were performed on days 30 and 66 of lactation in each treatment. Blood samples were collected fortnightly to analyse non-esterified fatty acids (NEFA) by an enzymatic colorimetric method, and twice weekly to determine progesterone concentrations by radioimmunoassay. Cow LW losses (P < 0.05), fat-corrected milk yield (P < 0.05) and calf average daily gain (P < 0.01) during lactation were higher in ADLIB. Nursing frequency affected the mean serum concentrations of NEFA, being lower in RESTR1 (0.18 mmol/l; P < 0.05) than in RESTR2 and ADLIB cows (0.29 and 0.25 mmol/l, respectively). The highest occurrence of nursing bouts was observed in ADLIB, leading to greater nursing duration per day (not statistically compared) in this treatment (58.8 ± 5.84 min) than in their restricted nursing counterparts (22.2 ± 1.42 and 34.3 ± 1.16 min, in RESTR1 and RESTR2, respectively). The nursing system did not affect the proportion of cows cycling within 3 months post partum (58%, 46% and 55% in RESTR1, RESTR2 and ADLIB, respectively; P > 0.05). The majority of cows in all treatments showed a short oestrus cycle after first ovulation (75%, 100% and 83%; P > 0.05). In conclusion, the post-partum luteal function in cows managed under continuous access to calves was similar to restricted nursing frequencies, despite the greater suckling intensity of the formers. Restricting calf presence does not enhance the resumption of ovarian activity when suckler cows are managed in moderate nutritional conditions.     

Short estrous cycles and associated serum progesterone levels in beef cows

Short estrous cycles in beef cows were investigated in two experiments. In trial 1, breeding dates from 2,854 fall-calving Angus cows were used to determine the incidence of short estrous cycles. Of 198 cycles of less than 17 days, 170 were between the first and second detected estrus. Estrous cycles of 7 to 10 days occurred more frequently (P<.005) than other short estrous cycles. Eight-day estrous cycles were most frequent. In the second experiment, calves were weaned from 25 of 33 anestrous spring-calving, crossbred Simmental cows. Compared to herdmates still nursing calves, an increased percentage of cows which had calves weaned were observed in estrus within 10 and 25 days after the date of weaning (P<.005) and a higher percentage had 7- to 10-day estrous cycles. Cows that were observed in estrus within 10 days after weaning were inseminated with Angus semen at their first estrus and with Simmental semen at their second estrus. No cows conceived on the first estrus of 7- to 10-day estrous cycles; 61.5% conceived on the second estrus. Serum progesterone was higher (P<.01) before the second estrus than the first.     

AGE AND LENGTH AT WEANING AND DEVELOPMENT OF DIET OF PANTROPICAL SPOTTED DOLPHINS, STENELLA ATTENUATA, FROM THE EASTERN TROPICAL PACIFIC

Using stomach contents from 203 spotted dolphins ( Stenella attenuata ) killed in the yellowfin tuna fishery, we modeled the weaning process of calves. Spotted dolphins began to take solid food at approximately 6 mo of age, or 115 cm, but continued to suckle until they were nearly 2 yr old. Calves tended to feed more frequently on squid as they got older, which suggested there was a shift in diet during weaning. The average age and total body length at weaning was estimated to be 0.8 yr (approximately 9 mo) and 122 cm. The oldest suckling calf was almost 2 yr old, which suggests that some calves continued to suckle for more than a year after they could have been weaned. A better understanding of the weaning process, especially quantifying the period of time when calves are nutritionally dependent on their mothers may lead to a better evaluation of their potential vulnerability to the disturbance caused by the yellowfin tuna purse-seine fishery.     

Short communication: administering an appeasing substance to Bos indicus-influenced beef cattle at weaning and feedlot entry

The bovine appeasing substance (BAS) is expected to have calming effects in cattle experiencing stressful situations. Therefore, this study investigated the impacts of BAS administration during two of the most stressful events within beef production systems: weaning and feedlot entry. In experiment 1, 186 Bos indicus-influenced calves (73 heifers, 113 bulls) were weaned at 211 ± 1 days of age (day 0). At weaning, calves were ranked by sex and BW, and assigned to receive BAS (Nutricorp, Araras, SP, Brazil; n = 94) or water (CON; n = 92). Treatments (5 ml) were topically applied to the nuchal skin area of each animal. Calf BW was recorded and samples of blood and tail-switch hair were collected on days 0, 15 and 45. Calves that received BAS had greater (P < 0.01) BW gain from day 0 to 15 compared with CON. Overall BW gain (days 0 to 45) and BW on days 15 and 45 were also greater (P ≤ 0.03) in BAS v. CON. Plasma haptoglobin concentration was less (P < 0.01) in BAS v. CON on day 15, whereas cortisol concentrations in plasma and tail-switch hair did not differ between treatments (P ≥ 0.13). In experiment 2, 140 B. indicus-influenced bulls (∼27 months of age) from 2 different pasture-based systems (70 bulls/origin) were transported to a commercial feedlot (≤ 200-km transport; day -1). On day 0, bulls were ranked by source and BW, and assigned to receive BAS (n = 70) or CON (n = 70) and the same sampling procedures as in experiment 1. Bulls receiving BAS had greater (P = 0.04) BW gain from day 0 to 15, but less (P < 0.01) BW gain from day 15 to 45 compared to CON. No other treatment effects were detected (P > 0.14). Therefore, BAS administration to beef calves alleviated the haptoglobin response associated with weaning, and improved calf growth during the subsequent 45 days. Administration of BAS to beef bulls at feedlot entry improved BW gain during the initial 15 days, but these benefits were not sustained throughout the 45-day experiment.     

Effects of castration and weaning conducted concurrently or consecutively on behaviour,blood traits and performance in beef calves

The objectives of this study were to evaluate the effects of Burdizzo castration and abrupt weaning on the behaviour, blood traits and performance of beef calves when weaning was conducted concurrently or consecutively to castration. In total, 64 male beef calves aged between 6 and 7 months were assigned to a 2×2 factorial design with the following treatment groups (n=16 animals per treatment): (1) castrated and concurrently weaned in week 0 (CAS-WEA); (2) castrated in week 0 and weaned in week 4 (CAS-CON); (3) bulls weaned in week 0 (BUL-WEA); and (4) bulls weaned in week 4 (BUL-CON). The behaviour of the calves was observed for 3 days following weaning. Blood was collected weekly from weeks 0 to 5 and analysed for the acute-phase protein haptoglobin, and neutrophil and lymphocyte percentages. BW was recorded weekly from weeks 0 to 7. Animals were slaughtered at 17 months and weight, dressing percentage and carcass classifications were recorded. On day 1 after weaning, the number of vocalizations (calls/10 min) was higher in BUL-WEA (7.2) and CAS-WEA (5.4) than in calves of CAS-CON (2.8) and BUL-CON (2.9) groups (P<0.05). From days 1 to 3 vocalizations decreased in all groups. CAS-CON and BUL-CON animals spent 20% lying on day 1 after weaning compared with 40% in CAS-WEA and BUL-WEA calves (P<0.05). The haptoglobin concentration decreased during the first 5 weeks after weaning in all groups independent of the castration, weaning group or its interaction (P>0.05). WEA groups showed an increased average daily gain (ADG) during weeks 0 to 3 and a reduced ADG during 4 to 7 weeks in comparison with CON animals. At slaughter, bulls were about 80 kg heavier than castrates and had a superior dressing percentage and carcass classification (P>0.05). In conclusion, weaning had a greater effect on the number of vocalizations, standing/walking and lying behaviour and ADG compared with Burdizzo castration. In comparison with undertaking the procedures separately, concurrent castration and weaning neither affected behaviour and haematological parameters nor impaired performance. There was no evidence that the concurrent application of both treatments markedly increased the stress response compared with their application at intervals of a few weeks.     

Performance of ad libitum fed dairy calves weaned using fixed and individual methods

The increasing availability of automated milk dispensers on dairy farms facilitates ad libitum milk supply but weaning calves from high milk allowances is challenging. This study evaluated effects of gradual weaning methods on starter intake, growth, selected blood parameters and weaning distress in ad libitum fed dairy calves during weaning and early post-weaning periods. Thirty-six male Holstein (n = 30) or crossbred (n = 6) calves were individually housed from days 2 to 14 of age and had ad libitum access to milk replacer (MR) from teat buckets. From days 15 to 84 of age, calves were grouped and had ad libitum access to MR, starter, straw and water from automated feeders. At day 35, calves were blocked (age and breed), and randomly assigned to a weaning method: (1) linear fixed (LIN), MR supply was stepped down to 6 l/day on day 36, and linearly reduced between days 36 to 63 from 6 to 2 l/day. (2) Step-down (STEP), MR supply was stepped down to 6 l/day from days 36 to 48, 4 l/day from days 49 to 56 and 2 l/day from days 57 to 63. (3) Dynamic (DYN), at day 36, MR supply was reduced for each individual calf to 75% of the average voluntary consumption between day 29 and 35, then maintained for 9 days, reduced to 50% for 10 days, and to 25% for 9 days. The DYN calves received more MR during weaning than LIN calves, whereas STEP calves had intermediate MR intake. Starter intake was not affected by weaning method. The DYN calves (1.33±0.08 kg/day) grew faster and were heavier than STEP calves (1.10±0.08 kg/day) during post-weaning period, whereas no difference was observed between LIN calves (1.23±0.08 kg/day) and others. At days 70 and 84, concentrations of β-hydroxybutyric acid were higher in LIN calves compared to STEP and DYN calves. Hair cortisol concentrations were not affected by weaning method. During the gradual weaning process CP intake seemed to recovered earlier than metabolizable energy (ME) intake in all treatments, suggesting that ME rather than CP could be the first limiting factor for growth during weaning. These results highlight the post-weaning benefits of DYN and LIN weaning methods when compared with more abrupt step-down strategies.     

Developmental gene expression of lactoferrin in duodenum and effect of weaning age on gene expression of lactoferrin in piglets

Two experiments were conducted to evaluate duodenal gene expression of lactoferrin and effect of weaning age on mRNA expression of lactoferrin in piglets using semi-quantitative RT-PCR analysis. In experiment 1, a total of 15 female Duroc x Landrace x Yorkshire piglets of five groups, each group pigs at 1, 14, 28, 42 and 56 days of age were used to determine developmental gene expression of lactoferrin in duodenum. In experiment 2, a total of 18 female neonatal piglets were divided into three groups, which were weaned at 21, 28 and 35 days of age respectively. In each group, three piglets' duodena were sampled at 21, 28 and 35 days of age and the other three piglets' duodena were sampled 7 days after weaning in each group. The samples were collected for detecting the effect of weaning age on lactoferrin mRNA expression of piglets. The results show that lactoferrin mRNA levels decreased steadily in postnatal day 1-56. But only from day 28-42 (14 days after weaned), the levels of lactoferrin gene expression were decreased markedly (p < 0.05), and the difference of lactoferrin mRNA levels at other stages was not significant. This result suggested that weaning had an effect on gene expression of lactoferrin. The results of experiment 2 showed that when the piglets were weaned at 21-28 and 35 days of age respectively, the expression levels of lactoferrin were decreased by 77%, 53% and 59% at the seventh day after weaning. Our results showed that weaning significantly decreased lactoferrin mRNA expression of piglets.     

Plasma and tissue levels of digestive regulatory peptides during postnatal development and weaning in the calf.

Changes in the concentrations of cholecystokinin, gastric inhibitory peptide, gastrin, motilin, pancreatic polypeptide, secretin, somatostatin, and vasoactive intestinal peptide in calf plasma and antral, duodenal and/or pancreatic tissues were assessed by radioimmunoassay during postnatal development and after weaning in 50 male Holstein-Friesian calves (randomly distributed into 10 groups of 5 animals each). The calves in the first group were killed at birth while those in 6 other groups were colostrum-fed for 2 days and then milk-fed until 7, 28, 56, 70 or 119 days of age. Those in the remaining 3 groups were given the same diets until day 28, were then weaned between day 29-56, and slaughtered on days 56, 70 or 119. In milk-fed animals, changes in plasma and tissue concentrations of almost all digestive regulatory peptides were observed during the 1st month of postnatal life, especially at day 2. Weaning was accompanied by variations in the plasma concentrations of somatostatin, secretin, gastrin, pancreatic polypeptide and gastric inhibitory peptide but not by any apparent change in peptide tissue concentrations (except VIP in the duodenum). Thus, the variations in tissue concentrations are primarily age-related, while plasma concentrations were modified by age and weaning.