A study was conducted to evaluate the effects of different dietary energy levels on the
productive (ADG, FCR, body weight, carcass) and reproductive (scrotum, testes, semen)
characteristics of young Dorper rams. The study was carried out in two phases at the University
of the Free State campus in Bloemfont ein, South Africa. Out of a group of 60
rams, 36 animals that were successfully trained for semen collection with the aid of an
artificial vagina (AV), were selected to be part of this study and housed in individual metabolic cages. During phase 1 of this study, 36 (11 to 12 months old) Dorper rams with a mean initial
body weight of 42.0 ± 0.52kg were randomly allocated to 3 groups (n=12 per group).
Each group was randomly assigned to one of 3 experimental diets (treatments), formulated
on a crude protein, degradable protein, calcium and phosphorus equivalent basis. A
medium energy (Me) diet was formulated according to the National Research Council
standards (NRC) for young growing rams to serve as the control diet. The metabolisable
energy (ME) content of this diet (Me) was increased by 15 % for the high energy (He)
and decreased by 15% for the low energy (Le) diets respectively. The actual ME levels
for the Le, Me, He: were 6.52, 8.09 and 9.39 MJ/kg, respectively. The rams received the
diets and fresh water ad libitum during a 127 day trial period and were weighed once a
week. Their ADG, FCR and ME/kg weight gain calculated and compared amongst
groups.
During this trial, a digestibility trial was conducted for 7 days (during week 14 of the trial),
using 5 randomly selected animals from each treatment group. The amount of feed
offered and consumed by each animal as well as the feaces excreted daily were recorded.
The chemical composition of the diets and the feaces (dry matter, energy, crude and degradable
protein) were determined.
Semen was collected from each ram, every forthnight for 3 consecutive days, with the aid
of an AV and evaluated for volume, overall sperm motility, forward progression, sperm
concentration, % live sperm and % normal sperm. The semen samples were then diluted
(using a one-step dilution method with a cryodiluent containing 5% glycerol), packed in 0.25ml plastic straws, equilibrated for 4 hours and cryoperserved (frozen) in liquid nitrogen
vapour (-70 ºC).
One week after freezing, the semen was thawed (38 ºC for 30 seconds) and evaluated for
the same qualitative parameters as the fresh semen. The results were compared amongst
groups for each collection time, using ANOVA for repeated measures analysis procedures
of SAS. The energy level of the diet and the collection week as well as their interaction
was used as independent variables, while the different semen parameters cons idered
were the dependent variables in the model. When means differed significantly, the
Tukey method was used to compare means.
At the end of this trial period, 6 rams per group were randomly selected and slaughtered
at a commercial abbatoir. After slaughtering the carcass characteristics (cold carcass
weight, dressing percentage, carcass grade, shoulder circumference, buttock circumference,
backfat thickness, eye muscle area, marbeling and kidney fat) were recorded and
compared amongst groups. The scrotum (total weight, skin weight, fat and circumference),
testes (volume and weight) and epid ydimis (weight and volume) characteristics were
also recorded and compared between groups, using ANOVA procedures of SAS. When
means differed significantly the Tukey method was used to compare means.
From the independent variables considered in the model, only the diet (ME level) had a
significant effect on the parameters considered. In general, an increase in dietary energy
level resulted in higher growth rates, better feed conversion rates, heavier carcasses, higher dressing percentages and greater fat deposition, both in the carcass, around the kid neys
and in the scrotum (particularly in the neck region, over the testicular vascular cone).
It seems that the energy requirements recommended by the NRC (1985) are not applicable
for early mature Dorper replacement ram lambs, as those in the He group, (real ME
level similar to NRC recommendations) deposited excessive fat in their body. Despite
the significant differences induced by the He on the growth performance, carcass characteristics
as well as on the scrotal and testicular characteristics of Dorper rams, no detrimental
effects were recorded in their semen quantity, quality and cryotole rance.
During the following 90 days (phase 2), the remaining rams (n=6 per group) were further
maintained on the Le diet for 90 days. This was done to simulate the situation when overconditioned
(fat) rams bought at auctions are placed on low energy diets (veld). Other
objectives of this trial phase were to evaluate if the fat deposits accumulated in the scrota
of rams fed on high energy diets are mobilized during subsequent periods of moderate
nutritional restriction and if these nutritional restrictions induce any changes on the semen
characteristics of rams.
During this phase of the trial, semen was collected, with the aid of an AV, every 3 weeks
during 2 consecutive days. The semen was evaluated using the same procedures described
for phase 1 of this study. The rams were slaughtered at the end of this trial period
(90 days) at a commercial abattoir. After slaughtering, the carcass characteristics (cold
carcass weight, dressing percentage, carcass grade, shoulder circumference, buttock circumference,
backfat thickness, eye muscle area, marbeling and kidney fat), the testicular (volume and weight), the scrotal (weight, circumference, skin weight and fat) and the epididymis
characteristics (weight and volume) were also recorded and compared amongst
groups. Data was analysed statistically using the same procedures as described for phase
1.
The results of this trial clearly indicated that the scrotal fat deposits of rams previously
fed on the He diet are mobilized (at least partially) during subsequent periods of moderate
dietary energy restrictions without adverse effects on semen quantity and qua lity. This is
the first time that such finding is reported.
Further research on the effect of high energy diets on subsequent ram fertility (short and
long terms), as well as their reversibility are warranted. Different age groups, feeding
regimes and other management practices must also be associated to high energy diets in
order to fully evaluate the effect of these common practices on subsequent ram fertility.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-02192007-102239 |
| Date | 19 February 2007 |
| Creators | Bester, Nena |
| Contributors | Prof JPC Greyling, Prof HJ van der Merwe, Dr LMJ Schwalbach |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-02192007-102239/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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