Low Feeding Level Research Articles

Dairy cows’ reproductive response to feeding level differs according to the reproductive stage and the breed

Reproductive performance has decreased over the last decades in many dairy systems. This study aimed at comparing the effects of a high- and a low-feeding level on reproductive stages (cyclicity, oestrus and fertility) of Holstein and Normande cows in a grass-based winter compact calving system. High-fed cows received a total mixed ration composed of 55% maize silage, 15% dehydrated alfalfa pellets and 30% concentrate in winter and 4 kg/day concentrate supply at grazing. Low-fed cows only received 50% grass silage and 50% haylage in winter and no concentrate at grazing. Low-fed cows produced less milk over 44 weeks, but lost more body condition (BC) than high-fed ones (5207 v. 7457 kg, −1.28 v. −0.96 unit, P < 0.001). Normande cows produced less milk and lost less BC than Holstein ones (5596 v. 7068 kg, −0.89 v. −1.36 unit, P < 0.001). Post-partum ovarian activity was little affected by the feeding level. In both breeds, ovulation detection rate was higher in low-fed cows (74% v. 59%, P < 0.001) and detection relied more frequently on standing behaviour (67% v. 55%, P = 0.022). In both breeds, the recalving rate following the first and second inseminations was not significantly affected by the feeding level, although more non-fertilisations or early embryo mortalities occurred in low-fed cows (43% v. 26%, P = 0.004). For the Holstein breed, this was clearly explained by more late embryo mortalities in high-fed cows (30% v. 9%, P = 0.004). Finally, pregnancy rate by the end of the 13-week breeding period was similar between feeding groups. Conversely, the Normande dual-purpose cows had a higher pregnancy rate by the end of the breeding period than the Holstein dairy cows (72% v. 54%, P = 0.007), owing to a better ovarian activity (79% v. 54% normal, P < 0.001) and a higher recalving rate following insemination (53% v. 37%, P = 0.007). In conclusion, this study demonstrates that feeding levels with converse effects on milk yield and BC score also have converse effects on reproductive stages and lead to quite similar final reproductive performance in compact calving systems. Normande cows benefit from an overall better reproductive performance, but do not suit high feeding levels for very compact calving systems owing to depressed oestrous behaviour.

VOLATILE PROFILE AND SENSORY CHARACTERISTICS OF DRY‐CURED LOINS AS AFFECTED BY FEEDING LEVEL IN THE PERIOD PREVIOUS TO THE LATE FATTENING PHASE AND BY REARING SYSTEM OF IBERIAN PIGS

ABSTRACT The effect of a moderate feed restriction (50 g feed/kg LW0.75[low feeding level, L] versus 70 g feed/kg LW0.75[high feeding level, H]) during the period previous to the late fattening phase on chemical composition, volatile profile and sensory quality of Iberian dry‐cured loins from animals reared in free range (FR) or in confinement (C) along the fattening phase was studied. Total tocopherol, total free amino acid and ammonia contents of dry‐cured loins from pigs FRL and FRH were higher (P &lt; 0.05) than those from CL and CH. Sixty‐one volatile compounds were identified and semiquantified in the headspace of all dry‐cured loins. The FRL products showed the highest (P &lt; 0.05) amino acid catabolism volatile compounds. In the rank‐order test sensory analysis, the FR products obtained higher sums of ranks (P &lt; 0.05) than those from confinement. Appearance, flavor, odor and texture scores showed a similar trend (FRL ≥ FRH &gt; CL = CH).PRACTICAL APPLICATIONSDry‐cured products (loins and hams) from Iberian pigs that are reared at free range (FR) are highly appreciated by consumers, reaching the highest price. The feeding level of the Iberian pig in the period previous to the late fattening phase affects the amount of amino acid catabolism volatile compounds of dry‐cured loins from pigs reared at FR which is reflected in a better sensorial quality of the dry‐cured loin. A moderate feed restriction during the period previous to the late fattening phase of Iberian pigs reared at FR could be a good strategy to improve the sensory quality of dry‐cured products.

Ytterbium oxide has the same accuracy as chromic oxide for estimating variations of faecal dry matter output in dairy cows fed a total mixed ration at two feeding levels

Daily herbage intake by ruminants at grazing can be estimated from faecal output and herbage digestibility. Chromic oxide has long been used as an external marker to estimate faecal dry matter (DM) output. The aim of this experiment was to determine the performance of ytterbium oxide compared to chromic oxide as an external marker for estimating variations of faecal DM output in dairy cows. Both markers were compared on eight Prim’Holstein lactating dairy cows, of which four were fistulated. Cows were offered a total mixed diet based on maize silage either at 100% or 70% of ad libitum DM intake, according to a single 2 × 2 reversal design with 2 experimental periods of 3 weeks. Faecal recovery of markers was determined over the last five days of each period by total faecal collection or by faecal sampling only during milking times. The between-day and the within-day variability of faecal marker concentrations were also investigated, as well as the between-day variability of faecal marker concentrations during the transition between periods 1 and 2. Both markers over-estimated the actual faecal DM output due to an incomplete faecal recovery. The average faecal recovery was slightly greater for Yb than for Cr (0.93 vs. 0.89). Faecal recovery of Yb and Cr was unaffected by feeding level irrespective of the faecal collection method. Ytterbium showed similar between-day and within-day variability of faecal concentration as Cr during the experiment (steady-state period), and similar between-day variability of faecal concentration as Cr during the transition period (non steady-state period). We conclude that ytterbium oxide used as a digestive marker seems to have the same accuracy as chromic oxide for estimating daily faecal DM output variations in dairy cows fed a total mixed ration, at low and high feeding level.

ORIGINAL ARTICLE: Impact of feeding level on digestibility of a haylage-only diet in Icelandic horses

Eight mature Icelandic geldings were used in an experiment arranged as a change-over design to evaluate the effect of feeding level on the digestibility of a high-energy haylage-only diet. The horses were fed a low feeding level 10.7 g dry matter (DM)/kg body weight (BW) (maintenance) and a high feeding level 18.1 g DM/kg BW (1.5 × maintenance) during two 23 days experimental periods. Total collection of faeces was performed for 6 days at the end of each period to determine the coefficient of total tract apparent digestibility (CTTAD). The CTTAD for DM, organic matter, neutral detergent fibre (NDF), acid detergent fibre and energy was higher in horses fed at the low level of feed intake, while feeding level did not affect the CTTAD of crude protein. The largest difference in CTTAD between feeding levels was found for NDF. The content (/kg DM) of digestible energy in the haylage was 11.3 MJ at the low level of feed intake and 10.6 MJ at the high level of feed intake. It can be concluded that feeding level has a large impact on the digestibility and energy value of early cut haylage in Icelandic horses.

Dietary energy source and feeding levels during the rearing period affect ovarian follicular development and oocyte maturation in gilts

Fifty-four Landrace × Yorkshire gilts (59.0 ± 4.2 kg and 147 ± 3 d old) were used to examine the effects of dietary energy source (starch or mixed fat) at high [112.5% of energy requirements recommended by NRC (1998)], normal (100%), and low (87.5%) energy feeding levels on ovarian follicular development and oocyte maturation. Forty-seven estrus gilts were slaughtered at Day 19 after the second estrus; oocytes were recovered from follicles >4 mm in diameter, and matured in vitro for 44 h. Gilts fed high-energy diets had more follicles >4 mm (mean, 25.8 vs. 19.1, P < 0.05) and more oocytes that reached metaphase II (80.3 vs. 64.0%, P < 0.05) than those fed the low-energy diet. Furthermore, gilts fed starch-rich diets had enhanced oocyte nuclear maturation relative to those fed fat-rich diets (75.4 vs. 68.0%, P < 0.05). Compared to the lower-energy feeding groups, high-energy feeding groups had higher ( P < 0.05) blood concentrations of postprandial insulin (1562.4 vs. 990.0 ng/4 h), IGF-I (321.2 vs. 256.9 ng/mL), and LH pulses (2.7 vs. 1.4 pulses/6 h). Follicular fluid concentrations of IGF-I (198.5 vs. 143.1 ng/mL) and estradiol (152.6 vs. 124.8 ng/mL) were higher ( P < 0.05) in the high-energy group than in the normal group. Compared with gilts fed the high-energy diet supplemented with fat, gilts fed the high-energy diet supplemented with starch had a tendency ( P < 0.10) towards increased IGF-I concentration in both blood and follicular fluid, and improved oocyte nuclear maturation during culture in vitro. We inferred that starch-rich, high-energy diets during rearing may improve ovarian follicular development and oocyte maturation in replacement gilts.

Effect of feeding allowance level on embryonic survival, IGF‐1, insulin, GH, leptin and progesterone secretion in early pregnancy gilts

The present experiment was conducted to evaluate the effects of feeding allowance level on embryonic survival, uterine development and reproductive hormone secretion in early gestation gilts. A total of 54 F1 crosses of Landrace x Large white gilts were randomly allocated to three treatment groups of high (H, 2 x maintenance), medium (M, 1.2 x maintenance) and low (L, 0.6 x maintenance) feeding level after mating. Blood samples and uterine flushings were collected on day 12, 25 and 35 of pregnancy, and embryonic survival rate was estimated. Concentrations of insulin-like growth factor I (IGF)-1, insulin, growth harmone (GH), leptin and progesterone in serum and uterine flushings were determined by enzyme-linked immunosorbent assay. Embryonic survival was affected by dietary treatment; total number of viable embryos and embryo survival of group M were higher than other groups in the early pregnancy (p < 0.05). Greater foetal weight in M gilts was achieved when gestation advanced to day 35 (p < 0.05), though there was no difference on day 25 of pregnancy among treatments. No appreciable differences were observed in the crown-rump length on day 25 and 35 of pregnancy among groups. Greater weight of uterus and products of conception were identified in M gilts compared with group H and L (p = 0.024 and p = 0.005, respectively) on day 25 of pregnancy. The hormone level was greatly affected by feeding allowance level. In serum, concentrations of IGF-1, leptin and insulin tended to be greater in H than in M and L during the early gestation, while concentrations of GH were greater in M and progesterone were the lowest in H. At the same time, feed allowance level affected the concentration of IGF-1, insulin, GH, leptin and progesterone in uterine flushings. These data demonstrated that feed allowance level after mating has important consequence on embryo survival, embryo development and uterine development, possibly mediated by nutrition level inducing changes in concentrations of reproductive hormones and/or intermediary metabolites in early pregnancy.

A validated genome wide association study to breed cattle adapted to an environment altered by climate change.

Continued production of food in areas predicted to be most affected by climate change, such as dairy farming regions of Australia, will be a major challenge in coming decades. Along with rising temperatures and water shortages, scarcity of inputs such as high energy feeds is predicted. With the motivation of selecting cattle adapted to these changing environments, we conducted a genome wide association study to detect DNA markers (single nucleotide polymorphisms) associated with the sensitivity of milk production to environmental conditions. To do this we combined historical milk production and weather records with dense marker genotypes on dairy sires with many daughters milking across a wide range of production environments in Australia. Markers associated with sensitivity of milk production to feeding level and sensitivity of milk production to temperature humidity index on chromosome nine and twenty nine respectively were validated in two independent populations, one a different breed of cattle. As the extent of linkage disequilibrium across cattle breeds is limited, the underlying causative mutations have been mapped to a small genomic interval containing two promising candidate genes. The validated marker panels we have reported here will aid selection for high milk production under anticipated climate change scenarios, for example selection of sires whose daughters will be most productive at low levels of feeding.

Ecophysiology of polyphosphate-accumulating organisms and glycogen-accumulating organisms in a continuously aerated enhanced biological phosphorus removal process

To investigate the ecophysiology of populations of polyphosphate-accumulating organisms (PAO) and glycogen-accumulating organisms (GAO) in communities of a novel acetate fed process removing phosphate from wastewater. Attempts were made to see if acetate could be replaced by an alternative carbon source which did not support the growth of the GAO. A continuously aerated sequencing batch reactor was operated with different acetate feed levels. Fluorescence in situ hybridization (FISH) showed that Defluviicoccus GAO numbers increased at lower acetate feed levels. With FISH/microautoradiography (MAR) both detected morphotypes of Defluviicoccus assimilated a wider range of substrates aerobically than Accumulibacter PAO. Their uptake profile differed from that reported for the same phylotype in full scale anaerobic : aerobic EBPR plants. This suggests that replacing acetate with another substrate is unlikely to provide Accumulibacter with a selective advantage in this process. Why Defluviicoccus appeared to out-compete Accumulibacter at lower acetate concentrations was not clear. Data suggest physiological and morphological diversity may exist within a single Defluviicoccus phylotype. This study implies that the current FISH probes for Defluviicoccus GAO may not reveal the full extent of their biodiversity, and that more information is required before strategies for their control can be devised.

Effect of pregnancy and feeding level on cell turnover and expression of related genes in the mammary tissue of lactating dairy cows

Milk yield is reduced by pregnancy, and the present experiment was conducted to study the biological basis for the negative effect of pregnancy on milk yield. A total of 16 dairy cows were fed at either a normal or a low feeding level (eight cows per treatment), and half of them were inseminated after approximately 3 months of lactation and the other half were not inseminated. Mammary biopsies were taken at approximately 9 months of lactation. The milk yield of pregnant cows was reduced by 2.6 kg/day, and lactation persistency was reduced already from the time of insemination. Low feeding level reduced the milk yield by 9.8 kg/day from week 8 to week 39 of lactation, whereas no interaction between pregnancy and feeding level was found. Cell proliferation (Ki-67) and apoptosis (terminal deoxynucleotidyl transferase dUTP nick end labeling, TUNEL) were unaffected by feeding level, and pregnancy tended to reduce cell proliferation but had no effect on apoptosis. Reduced cell proliferation may explain the reduced lactation persistency in pregnant cows. Transcription of oestrogen receptor α, progesterone receptor A and B, and long and short isoforms of the prolactin receptor were higher in pregnant cows compared with non-pregnant cows. Feeding level did not mediate changes in transcription of genes. Transcription of other cell-turnover-related genes (IGF-I, IGF binding protein-5, caspase-3) as well as genes related to the secretory activity of the cells (α-lactalbumin and acetyl CoA carboxylase α) was not affected by pregnancy or by feeding level.

The effects of grain treatment, grain feed level and grass silage feed value on the performance of and meat quality from, finishing beef cattle

A completely randomised design study involving 132 continental crossbred beef steers was undertaken to evaluate the effects of method of grain treatment and feed level, and grass silage feed value on animal performance, carcass characteristics and meat quality of beef cattle. Winter wheat was harvested and the grain was stored either ensiled crimped and treated with 4.5 l/t of a proprietary acid-based additive (crimped), ensiled whole and treated with 20 kg feed-grade urea per t (urea) or stored conventionally in an open bin treated with 3 l propionic acid per t. Two grass silages, of contrasting feed value (L and H) were ensiled. For the conventional, crimped and urea treatments, grain dry matter (DM) concentrations were 802, 658 and 640 g/kg, respectively. For the L- and H-feed value silages, DM concentrations were 192 and 240 g/kg and D values were 671 and 730 g/kg DM, respectively. The silages were offered as the sole forage supplemented with either conventional, crimped or urea-treated grain-based concentrate at either 3.5 or 6.0 kg DM per steer per day. The grain supplement consisted of 850 and 150 g/kg DM of grain and citrus pulp, respectively. For the conventional, urea and crimped treatments, DM intakes were 8.85, 9.43 and 9.04 kg/day (standard error (s.e.) = 0.129); estimated carcass gains were 0.60, 0.55 and 0.61 kg/day (s.e. = 0.020), respectively. For the low- and high- feed value grass silages, estimated carcass gains were 0.56 and 0.61 kg/day (s.e. = 0.014), respectively. For the low and high grain feed levels, estimated carcass gains were 0.56 and 0.61 kg/day, respectively. Grain treatment, grain feed level or silage feed value did not alter (P > 0.05) meat quality, lean colour or fat colour. There were significant silage feed value × grain feed level interactions (P < 0.05) for final live weight (LW) and daily live-weight gain (DLWG). Increasing grain feed level increased final LW and DLWG when offered with the low-feed value silage, however, grain feed level had no effect on final LW or DLWG when offered with the high-feed value silage. It is concluded that urea treatment of grain increased silage intake and feed conversion ratio (kg DM intake per kg carcass) and tended to decrease carcass gain. Crimping provides a biologically equally effective method to store grain as conventional methods. Improving grass silage feed value had a greater impact on animal performance than increasing grain feed level by 2.4 kg DM per day.

Effects of feeding, stocking density and water-flow rate on fecundity, spawning frequency and egg quality of Nile tilapia, Oreochromis niloticus (L.)

This study investigated the effects of two levels of feeding (1 or 4% BW day−1), two levels of stocking densities (3 or 10 female m−2) and two levels of water-flow rates (0.06±0.00 or 0.35±0.04 L s−1) on the fecundity, relative fecundity, spawning frequency and egg quality of Nile tilapia, Oreochromis niloticus (L.) with the goal of improving hatchery seed production. Males and females, 125 days of age, were stocked in recirculating concrete tanks. Eggs were collected every four days directly from the mouths of incubating females. Fecundity (eggs spawn−1), body weight gain (g day−1) and egg diameter (mm) and weight (mg), percent protein and lipid, fertilization and hatchability were measured over 120 days. Higher eggs kg female−1 day−1 (312±36) was observed in treatments with lower levels of stocking density (3 female m−2) and water-flow rate (0.06±0.00 L s−1) under both feeding rates. The rate was 2 to 4 fold higher than the others. Overall, high feeding level (4% BW day−1) increased growth (g day−1) by 35% and eggs spawn−1 by 18% and did not affect eggs kg female−1 day−1, spawn female−1 and eggs m−2 day−1. Higher stocking density (10 female m−2) lowered eggs spawn−1 by 19%, eggs kg female−1 day−1 by 52% and spawn female−1 by 40%. Higher water-flow rate (0.35±0.04 L s−1) increased growth (g day−1) by 33%, and lowered eggs kg female−1 day−1 by 51%. The variables also did not affect percent egg fertilization, hatchability, crude lipid and protein or egg diameter (mm). However, egg weight (mg) was higher in groups fed a lower ration (1% BW day−1) with higher stocking density (10 female m−2) and higher water-flow rates (0.35±0.04 L s−1). Feeding levels interacted with water-flow rates in improving growth (g day−1) while stocking density interacted with water-flow rates in lowering eggs kg female−1 day−1 and spawn female−1. The eggs kg female−1 day−1 obtained in this study from the best treatments is comparable with the highest egg production rates reported by others for O. niloticus. This suggests that lower feeding level (1% BW day−1), lower stocking density (3 female m−2) and lower water-flow rate (0.06±0.00 L s−1) could be adopted as a management strategy to improve current tilapia hatchery seed production, although, optimum water flow-related stocking density needs further investigation.

Effects of Trans-10, Cis-12 Conjugated Linoleic Acid on Ovine Milk Fat Synthesis and Cheese Properties

Trans-10, cis-12 conjugated linoleic acid (CLA) reduces milk fat synthesis in sheep in a manner similar to that seen in dairy cows, but its effects on cheese yield and flavor are unknown. Additionally, when dietary energy supply is restricted, CLA can increase milk and milk protein yield, which may alter cheese yield and eating quality. The objectives of the study were to examine the effects of supplementing ewe diets with a rumen-protected source of CLA at a high and low dietary energy intake on milk fat and protein synthesis and on cheese yield and eating quality. Sixteen multiparous ewes were randomly allocated to 1 of 4 dietary treatments: a high (6.7 Mcal of metabolizable energy/d) or low (5.0 Mcal of metabolizable energy/d) feeding level that was either unsupplemented or supplemented with 25 g/d of a lipid-encapsulated CLA (to provide 2.4 g/d of CLA) in each of 4 periods of 21 d duration in a 4×4 Latin square design. There was no effect of treatment on milk yield (g/d), but milk fat percentage and milk fat yield were reduced by 23 and 20%, respectively, in ewes supplemented with CLA. Milk fatty acid concentration (g/100g) of chain length <C16 was decreased and >C16 was increased in milk and cheese following CLA supplementation, whereas decreasing the feeding level increased fatty acids ≥C16. Milk fat contents of CLA were 0.01 and 0.12 g/100g of fatty acids for the unsupplemented and CLA-supplemented treatments, respectively, whereas cis-9, trans-11 CLA was unaffected by CLA supplementation. There was no main effect of treatment on cheese yield, which was 0.11±0.001kg of cheese/kg of milk, but cheese yield was highest, at 0.12±0.001 kg/kg, when made from milk of ewes fed the high feeding level + unsupplemented treatment. Cheese made from the milk of ewes supplemented with CLA, compared with the unsupplemented diet, was rated (scale 0 to 10) higher in the creaminess (2.1 vs. 1.4; SEM 0.15) and less oily (0.8 vs. 1.3; SEM 0.17) attributes, and was preferred overall (4.5 vs. 3.9; SEM 0.21). Cheese produced from sheep on the high vs. low feed level was rated less yellow (2.8 vs. 4.2; SEM 0.11), less salty (1.9 vs. 2.3; SEM 0.15), and more sour (1.5 vs. 1.1; SEM 0.13). We concluded that the effect of feeding level on animal performance and cheese characteristics was small, whereas supplementing the diets of ewes with a ruminally protected CLA source reduced milk fat yield, did not affect cheese yield, and beneficially altered the flavor characteristics of the cheese.

Starvation and low feeding levels result in an enrichment of 13C in lipids and 15N in protein of Nile tilapia Oreochromis niloticus L.

The influence of different feeding levels below and slightly above maintenance on whole body δ13C and δ15N values of Nile tilapia Oreochromis niloticus was examined. The energy budget of each fish was determined by indirect calorimetry. The δ13C values of the lipid‐free material of Nile tilapia fed below and slightly above maintenance level did not differ between the feeding groups, but the δ13C values in the lipids and the δ15N values of the lipid‐free material showed small but significant differences. Those fish with a negative lipid retention had significantly higher δ13C values in the lipid fraction compared to fish that synthesized fatty acids. There was a significant negative correlation between the amount of energy metabolized by the fish and both the δ13C values in the lipids and the δ15N values of the lipid‐free material. Fasting and feeding below the maintenance level may influence the isotopic composition of animals and should therefore be considered in ecological and nutritional studies.

Feeding level does not affect progesterone levels in intermittently suckled sows with lactational ovulation

The aim of this study was to examine whether the low post-ovulatory plasma P 4 levels found in intermittently suckled (IS) sows are related to the high feeding level during intermittent lactation. Multiparous sows ( n = 21) were separated from their piglets for 12 h per day starting at day 14 of lactation until 6 days after ovulation. At day 28 of lactation, 9 sows had ovulated (spontaneous) and the remaining 12 sows were treated with PG600 (PG600-induced). At ovulation sows were allocated to either a high (H) feeding level (on average 6.5 kg) or a low (L) feeding level (high feeding level minus 2.5 kg) until 6 days after ovulation. Plasma P 4 levels were not affected by feeding level or type of ovulation ( P > 0.10), and neither were CL parameters, embryo survival rate and embryo development at day 30 of gestation. In conclusion, low levels of plasma P 4 were found in IS sows with lactational ovulation but these were not affected by feeding level during the first week after ovulation. Further studies are needed to investigate which factors cause the lower plasma P 4 levels in these sows.

Relationship between rearing practices and eating quality traits of the muscle rectus abdominis of Charolais heifers

Ninety-nine Charolais heifers with an average age of 33 months and an average carcass weight of 381 kg were used to study the relationship between rearing practices and eating meat quality traits. Farm surveys were carried out to collect information about heifer rearing before weaning, during the growth period and during the finishing stage. The quality of meat from the M. rectus abdominis excised 24 h post mortem was scored between 0 and 10 by sensory analysis using four descriptors: initial tenderness, overall tenderness (OT), juiciness and flavour intensity. Intramuscular fat content was also measured. Four classes of rearing practices were differentiated by multiple correspondence analysis and hierarchical cluster analysis. The class 1 was based on a low feeding level during the growth period and a diet of hay and straw complemented with 8 kg of concentrates in the barn during the finishing period. A medium feeding level during the growth period and a finishing diet of grass at pasture and 6 kg of concentrates defined the class 3. The class 2 was linked to a high feeding level during the growth period and a supply of roughage and 6 kg of concentrates at pasture during the finishing stage. The class 4 was based on a high feeding level during the growth period and a finishing stage in the barn with maize silage and 5 kg of concentrates. There were no differences in meat juiciness and meat flavour intensity among the four practice classes. The classes 2 and 4 produced the tenderest meat (OT score: 5.5/10; p = 0.002), regardless of the finishing stage and the forage given to the animals. These classes were characterized by the highest feeding level, which allowed slaughter at a young age (32 months) resulting in the highest carcass weight (380 kg). The classes 1 and 3 classes were linked to the lowest tenderness (OT score: 4.8; p = 0.002) although the intramuscular fat content was equivalent to the classes 2 and 4 (17.8% in average). The classes 1 and 3 were characterized by a moderate growth period due to a low feeding level and a short finishing stage (108 to 135 days). Indeed, the finishing period did not allow the animals to recover the growth deficit brought about by the growth period. This type of farming practice required slaughter at a more advanced age (35.9 months) for equivalent carcass weights of 389 kg.

Effects of a mixed culture of common carp, Cyprinus carpio L., and Nile tilapia, Oreochromis niloticus (L.), on terrestrial arthropod population, benthic fauna, and weed biomass in rice fields in Bangladesh

Abstract A field experiment was conducted in order to assess the potential of common carp, Cyprinus carpio L., and Nile tilapia, Oreochromis niloticus (L.) to control arthropod population, benthos, and weeds in rice fields in Bangladesh. The two species of fish were stocked in mixed culture and provided with different inputs: regular urea fertilization, low feeding level, and higher feeding level. Rice only with regular fertilization was kept as a control. Fish significantly reduced the number of dipteran insects sampled by a vacuum suction device in rice fields, from an average of 6.6 m −2 to only 0.8, 1.0, and 1.0 m −2 in the three rice–fish treatments, respectively. No significant effects were found on the other species of insects identified. Benthos analysis revealed significant effects of fish on the abundance of molluscs, oligochaete worms and chironomid larvae. The effect of fish on total benthos abundance was somewhat weaker when fish where provided with a high feeding level, indicating that the supply of supplementary feed reduced the ingestion of natural feed in rice–fish culture. Fish were found to control the weeds in a rice field efficiently. Significant reduction of the weed biomass was observed in all three rice–fish treatments. Compared to rice grown alone, the weed biomass was reduced by 86% in rice–fish with urea fertilization, 85% in rice–fish with a low feeding rate, and 82% in rice–fish with a high feeding rate. In conclusion, fish can play a vital role in integrated pest management of insects and weeds.

The effect of level of feeding, genetic merit, body condition score and age on biological parameters of a mammary gland model

An evolutionary algorithm was applied to a mechanistic model of the mammary gland to find the parameter values that minimised the difference between predicted and actual lactation curves of milk yields in New Zealand Jersey cattle managed at different feeding levels. The effect of feeding level, genetic merit, body condition score at parturition and age on total lactation yields of milk, fat and protein, days in milk, live weight and evolutionary algorithm derived mammary gland parameters was then determined using a multiple regression model. The mechanistic model of the mammary gland was able to fit lactation curves that corresponded to actual lactation curves with a high degree of accuracy. The senescence rate of quiescent (inactive) alveoli was highest at the very low feeding level. The active alveoli population at peak lactation was highest at very low feeding levels, but lower nutritional status at this feeding level prevented high milk yields from being achieved. Genetic merit had a significant linear effect on the active alveoli population at peak and mid to late lactation, with higher values in animals, which had higher breeding values for milk yields. A type of genetic merit × feeding level scaling effect was observed for total yields of milk and fat, and total number of alveoli produced from conception until the end of lactation with the benefits of increases in genetic merit being greater at high feeding levels. A genetic merit × age scaling effect was observed for total lactation protein yields. Initial rates of differentiation of progenitor cells declined with age. Production levels of alveoli from conception to the end of lactation were lowest in 5- to 8-year-old animals; however, in these older animals, quiescent alveoli were reactivated more frequently. The active alveoli population at peak lactation and rates of active alveoli proceeding to quiescence were highest in animals of intermediate body condition scores of 4.0 to 5.0. The results illustrate the potential uses of a mechanistic model of the mammary gland to fit a lactation curve and to quantify the effects of feeding level, genetic merit, body condition score, and age on mammary gland dynamics throughout lactation.

Effect of level of feed restriction during growth and/or fattening on fatty acid composition and lipogenic enzyme activity in heavy pigs

The influence of feeding system on growth performance, carcass characteristics, and fatty acids profile of subcutaneous backfat and lipogenic enzymes activity was studied. The following feeding systems were applied: HH: group of 12 pigs fed with a high feeding level during growth and fattening periods; HL: group of 12 pigs fed with a high feeding level during growth period and a low feeding level during fattening period; LH: group of 12 pigs fed with a low feeding level during growth period and a high feeding level during fattening period; LL: group of 12 pigs fed with a low feeding system during growth and fattening periods. The high and low feeding levels applied during growth and fattening periods were 70 and 35 g feed/kg live weight 0.75 (LW 0.75) day and 121 and 87 g feed/kg LW 0.75 day, respectively. The duration of the growth period was 163 days in all groups. The ages at slaughter of HH, HL, LH and LL pigs were approximately 383, 406, 439 and 503 days, respectively. The HH and LL pigs had the higher and lower average daily gain respectively, while the LH pigs presented the best feed conversion ratio during fattening period. At slaughter, the LL pigs had the higher value of loin width and the lower values of backfat thicknesses and Longissimus dorsi muscle intramuscular fat percentage (P<0.05). The subcutaneous backfat outer and inner layers from LH and LL pigs had a significantly (P<0.05) higher proportion of C18:1 n-9 and ΣMUFA (monounsaturated) acids than those from HH and HL pigs. The subcutaneous backfat inner layer from LL pigs had a lower C16:0 and ΣSFA (saturated) acids proportions than those from remaining groups of pigs. The activity of the fatty acid synthase (FAS) and glucose-6-phosphate dehydrogenase (G6PD) enzymes, measured in subcutaneous backfat, at the end of growing period was significantly (P<0.05) higher in pigs fed high feeding level during growing phase. An increase of feeding level during the fattening phase led to an increase in the activity of G6PD enzyme. In conclusion, a marked effect of feeding system was observed on pig productivity and fatty acid composition.

Optimal decisions in organic beef production from steers — Effects of criterion of optimality and price changes

Organic beef production from steers demands several decisions concerning grazing strategy, feeding level in the winter and aspects as slaughter weight and length of the finishing period. A model has been developed to optimise these strategies. The objective of this study was (1) to find optimal strategies for organic beef production from steers regarding grazing strategy, feeding level in winter, finishing and slaughter in organic beef production from steer concerning economic output per time unit using a multi-level hierarchic Markov process and (2) to analyse the stability of these results by sensitivity analysis. The results showed that in general the optimal strategy only changes slightly depending on the criterion (net returns per steer versus per time unit). An optimization per time unit in some cases favours a more intensive production based on high feeding level in winter and finishing of steers as well as earlier slaughtering compared to an optimization per steer. Finishing of steers seemed not to be an optimal strategy from an economic point of view and price changes in feed, beef and premiums did not favour finishing of steers. Beef prices as well as prices for ryegrass/white clover pasture and low feeding level seemed to be the most important factors that influence net return.

Evidence for Different Nutrient Partitioning in Boran (Bos indicus) and Boran�נHolstein Cows When Re-allocated from Low to High or from High to Low Feeding Level

This study tested the hypothesis that purebred Boran (Bos indicus) cows and crossbreds of Boran and Holstein respond differently to long-term changes of feeding level in nutrient partitioning to milk and body fat stores. A total of 27 cows of these two genotypes were subjected either to a low or a high feeding level from their first oestrus as heifers until birth of their third calf. Half of the cows of each genotype were then switched to the other feeding level during the third reproduction cycle. If at all, Boran cows responded to a change in the feeding level almost exclusively by a corresponding change in body weight but not milk yield. Crossbred cows kept continuously on the low feeding level had a lower milk yield than those continuously fed the high level, but lost similar amounts of body weight. In crossbred cows, changing the feeding level from high to low was accompanied by a mobilization of body reserves, whereas a change from low to high level resulted mostly in an increase in milk yield. Certain other genotype differences in metabolic response were obvious from differences in body composition and from the metabolic profile either reflected in blood (particularly insulin-like growth factor I) or in adipose tissue (lipoprotein lipase). Reproductive performance differed between genotypes, with shorter lactations associated with earlier occurrences of the first oestrus in the Boran cows. Generally, feeding history appeared to have at least as much influence on energy partitioning as the actual feeding level. In conclusion, purebred Boran cows seem to react to long-term food fluctuations mainly by mobilizing and restoring body fat reserves, whereas cows crossbred with Holstein tend to spend extra energy preferentially for milk production.