Effect of qualitative feed restriction on energy metabolism and nitrogen retention in sheep

Periodic restrictions in feed quality and quantity is an important phenomenon in regions where animal production should bridge the gap between periods of forage production separated by a dry season. Eighteen Swifter male lambs, weaned at the age of ca. three months, were used to quantify effects of feed quality restriction and realimentation on changes in energy and nitrogen metabolism. The diet consisted of grass straw (17 MJ of gross energy [GE] and 46 g crude protein [CP] per kg dry matter [DM]) on an ad libitum basis and 35 g/kg0.75/d mixed concentrates (16.5 MJ of GE and 173 g CP per kg DM). At the age of ca. 3.5 months the animals were randomly divided into six blocks, based on live weight, according to a randomized complete block design. Within each block, the animals were randomly assigned to two restricted treatments (R1 and R2) and an unrestricted control (C) treatment. Treatments R1 and R2 were subjected to feed quality restriction by withholding the concentrate for 3 and 4.5 months, respectively. A modified linear model was developed to study the effects of restriction and realimentation. The comparison between treatments was made by analyzing the data of the R1 and R2 animals as deviations from the control animal in each block. During the restriction period, restricted animals lost weight and showed negative energy (EB) and nitrogen balances (NB), whereas their intake of low quality roughage increased significantly. During the realimentation period (5 and 6 months for the R1 and R2 animal, respectively), the R1 and R2 animals grew significantly faster than the control animals. The realimented animals persisted in ingesting significantly more low quality roughage and their EB and NB were significantly greater that those of the control animals. The R2 animals needed a longer period of realimentation because of a longer period of restriction. The expression of compensatory growth was mainly related to a sustained higher grass straw (low quality roughage) intake during the realimentation periods, and a significantly greater efficiency of metabolizable energy intake. The maintenance requirement of realimented animals was significantly lower only during the initial stages of realimentation compared with the controls. It seemed as if a three months feed restriction period in weaned sheep was better than 4.5 months

Prospects of compensatory growth for sheep production systems

The dry (lean) season imposes a natural feed restriction in grazing animals that must be compensated for during the wet (lush) season. The nutrition physiological backgrounds governing the changes during growth retardation and higher gain during compensation are obscure. Immature male lambs were used to determine the effects of feed quality restriction, i.e. feeding grass straw, on the pattern of feed intake, feed efficiency and growth, and changes in the physiological state of the animals. During restriction and following realimentation, the grass straw intake of the restricted animals was significantly higher than of their controls. Maintaining gut capacity was the main reason of ingesting more low quality feed. The delay in growth during the restriction period was fully compensated after realimentation with a significantly lower total feed consumption, while the carcass of the realimented animals was leaner than of the controls. Higher grass straw intake, lower maintenance requirements, an increased feed efficiency and changes in the composition of gain were mechanisms supporting compensatory growth. During the dry season with limited amounts of good quality feed available, imposing feed quality restriction is a useful strategy. During the following recovery period, animals compensate through increased feed intake and a more efficient use of the nutrients. Modelling the implementation of a strategy of compensatory growth indicated the possibility of a reduction of the total concentrate input by 40% per animal compared to an intensive system. Compared to an extensive system, only 35% of the rangelands is required, thereby reducing the grazing pressure on the rangelands and allowing regeneration of the vegetation species

Mycobiota and aflatoxin B1 contamination of rainbow trout (Oncorhinchus mykiss) feed with emphasis to Aspergillus section Flavi

In the present study, mycobiota and natural occurrence of aflatoxin B1 (AFB1) in pellet feed and feed ingredients used in a feed manufacturing plant for rainbow trout nutrition was investigated. The samples were cultured on the standard isolation media for 2 weeks at 28 ºC. Identification of fungal isolates was implemented based on the macro- and microscopic morphological criteria. AFB1 was detected using high performance liquid chromatography (HPLC). Based on the results obtained, a total of 109 fungal isolates were identified of which Aspergillus was the prominent genus (57.0%), followed by Penicillium (12.84%), Absidia (11.01%) and Pseudallscheria (10.10%). The most frequent Aspergillus species was A. flavus (60.66%) isolated from all feed ingredients as well as pellet feed. Among 37 A. flavus isolates, 19 (51.35%) were able to produce AFB1 on YES broth in the range of 10.2 to 612.8 µg/g fungal dry weight. HPLC analysis of trout feed showed that pellet feed and all feed ingredients tested except gluten were contaminated with different levels of AFB1 in the range of 1.83 to 67.35 µg/kg. Unacceptable levels of AFB1 were reported for feed including soybean, fish meal and wheat. These results indicate the importance of AF contamination of trout feed in amounts higher than the acceptable level as a risk factor for fish farming production