Micronutrient Nutrition of Breeding Birds: Part 2, Vitamins

 

By Rick Kleyn, MSc (Agric) Nutritionist, Avi-Products

 

In the previous article in this series I discussed the importance of minerals on breeding birds. In this issue the Vitamins mill be dealt with. Vitamins are truly micronutrients and their inclusion in the diet is measured in parts per million or less in the final diet. They are organic substances that are metabolically essential to the bird and the exclusion of a single vitamin from the diet can and does have dramatic effects. Mostly are unable to synthesis their own vitamins as they lack the necessary biochemical pathways. For this reason vitamins are particularly important in their role in fertility, hatchability and chick quality.

Before I go into a lot of detail about specific vitamins, there are some general aspects of vitamin nutrition that need to be discussed.

1) Vitamins are split into two distinct groups, the fat-soluble vitamins and the water-soluble vitamins.

 

The fat-soluble vitamins include the following:

Vitamin A (Retinol)

Vitamin D

Vitamin E

Vitamin K

All of these vitamins require some body fat for their metabolism. They are often present in plants as pro-vitamins, which are quickly converted to the true vitamins in the body of the animal. They are easily stored in fat cells and any excesses are excreted through the faeces.

 

The water-soluble vitamins are mainly needed for normal energy metabolism in the body, although we are becoming increasingly aware that they also play a role in protein metabolism. The important vitamins in the water-soluble group are:

 

Vitamin C (Ascorbic acid)            Pyridoxine (B6)
Thiamin (B1)                                 Riboflavin (B2) 
Biotin                                           Pantothenic Acid
Folic Acid                                     Niacin                
Vitamin B12                                   Choline

 

Apart from vitamin B12 birds are not able to store any of the water-soluble vitamins in their bodies, and therefor require all the water-soluble vitamins in their diet except Vitamin C, which they are mostly able to synthesise themselves. When a feed contains excess levels of the water-soluble vitamins they are excreted in the urine. For this reason, it is important that birds receive the correct level of these vitamins on a daily basis. It is precisely for this reason that humans are advised to take a vitamin tablet every day.

 

The significance of the difference between the classes of Vitamins is very clearly illustrated by work published by Prof. Steve Leeson form the University of Guelph in Canada. In this experiment, single vitamins were deleted from the diet of breeding hens, and were then reintroduced 15 weeks later. It is important to note firstly just how dramatic an effect the deletion of a single vitamin can be, particularly the water-soluble vitamins. Secondly, it is of interest that fertility returned to normal after 4 weeks, implying that no permanent damage was done.

 

Table 1: Hatchability of eggs produced by caged breeders fed diets devoid of supplemental vitamins (% fertile eggs)

 

Week on diet

Control

(all vits)

Biotin

Vit B12

Vit E

Folic Acid

Riboflavin

1

95

86

97

97

97

95

3

97

83

95

84

89

55

5

98

63*

84

67

30*

19*

7

92

54*

61*

62*

19*

1*

13

88

52

27*

95

38*

0*

15**

90

96

21*

75

70

0*

17

95

90

50*

58*

85

57*

19

97

99

99

92

99

96

* Significantly different from control

** Vitamins reintroduced

2) All vitamins, be they natural or synthetic are subject to degradation (oxidation) over time. High temperatures, UV radiation (sunlight), oxygen and moisture exacerbate this. Keeping food refrigerated or frozen helps, but research has shown that even the vitamin levels in frozen meat drop with time. It is essential therefore to use fresh vitamin sources at all time.

It is true that the ingredients we use to feed out birds do contain vitamins. The levels vary considerably from batch to batch as influenced by the growing conditions of the crop. It is also true that not all of the vitamins that occur in natural ingredients are available for use by animals. A good example of this is that almost all of the niacin found in cereal grain is unavailable to birds as it is boned to other components in the form of niacytin. For this reason, nutritionists tend to ignore the vitamins that occur in natural ingredients, and add the entire requirement in terms of supplementation.

3) Determining the level at which any animal’s diet should be supplemented with vitamins is a matter of debate amongst nutritionists. It is known that issues such as life stage (i.e. breeding) stress, parasite infestation, and infectious diseases also greatly increase the bird’s requirements. In addition, manufacturing processes such as extrusion and the time the product is likely to sit on a shelf are also important. In figure 1, the process that is followed is graphically illustrated. The NRC figure is the standard used by nutritionists to indicate the level at which deficiency symptoms no longer occur.

 

Figure 1: Optimum vitamin nutrition for animals (after Roche) 

 

(This graph couldn't upload please contact me if you require it)

 

4) It is important that we realise that as with the minerals, it is possible to feed birds too much. In work done in America on Bobwhite Quail, varying levels of vitamin A were offered to breeding birds. The results of this work are shown below.

 

Figure 2: Effects of vitamin A on survival and reproduction of captive Bobwhite Quail

 

 

It is of particular interest to note that for all parameters measured, a steady response was observed until a feeding level of about 8000 IU/kg was reached, at which point little improvement was noted. Perhaps of more interest, was the fact that a depression in hatchability was observed when levels exceed 12000 IU/kg.

 

In the case of breeding birds, there is a very clear relationship between the dietary vitamin levels and their concentration in the eggs of chickens. All of the vitamins have an impact on reproductive success and it is beyond the scope of this article to address the effects of each of the vitamins in turn, however there are some important issues that need to be raised. If you would like to do more reading on this subject, "Comparative Avian Nutrition" by Kirk Klasing covers the topic in great detail.

 

Vitamin A is the most likely vitamin to be deficient in either captive or wild birds. Plants do not contain Vit A itself, but rather a variety of carotenoids, which are the precursors of Vit A, and the levels that exist in most plants are extremely variable. High levels of Vit E (a natural anti-oxidant) have been shown to improve chick quality and boost humoral immunity. However, it has been shown that high levels of Vit E in the diet inhibit Vit A uptake and that if the Vit A levels are reduced, the uptake of Vit E improves.

 

Birds are able to synthesis Vit D in the presence of UV light. It has been shown that 15 minutes of normal sunshine per day will enable a laying hen to produce adequate amounts of Vit D. It is only under artificial lighting conditions that there is insufficient UV light and the bird needs to be supplemented.

 

Each of the B vitamins is essential to the production of healthy young, and it can be seen from table 1 just how sensitive to reduced levels of these vitamins birds are. Riboflavin (Vit B2) deficiency is know to result in classical curled toe paralysis, while a deficiency of biotin can lead to abnormal beaks (know as parrot beak) and deformed down (club down).

 

The entire Avi-plus range of feeds contain vitamin levels that are all well into the "optimal" range of supplementation. We have taken the losses in extrusion, together with a longer storage time than normal poultry feeds into consideration. As with is the case with the minerals, if you feed Avi-plus products in the recommended manner you will never need to supplement your diets with additional vitamins. If the inclusion of Avi-plus is reduced through adding additional seeds to the mixture, then there is a chance that you may dilute the amount of vitamins fed to your birds on a daily basis. If our products are mixed with any other ingredients we are no longer able to guarantee the adequacy of the diet.

 

There is an important rider that can be added to the above discussion, and this is best illustrated by an experiment that was conducted by Angel and Ballam in 1996. These workers fed 123 pairs of parakeets, four different diets. These were complete breeder diets containing 13, 18 and 25 percent protein, and a control diet, which was a mixture of seeds (white millet, canary seed and hulled oats), supplemented with both vitamins and minerals. The complete diets were identical apart from their differing protein levels and were supplemented with vitamins and minerals in the normal way. The breeding results that were achieved are shown in the table 2 below.

 

Table 2: Breeding performance and growth of parakeets.

 
 

Diet (Protein %)
 

13.5

18.2

25.0

13.4 (Seed)

Eggs/pair

15.2

14.1

15.2

12.2

Fertile eggs/pair

10.4

10.7

10.1

7.2

Hatched/pair

7.8

7.2

7.9

5.9

Weaned/pair

5.7

5.0

5.6

3.0

 

 

The important figure in table 2 is the number of babies weaned per pair. In scientific terms we would say that there was no significant difference between the 3 different complete diets and that a complete diet containing 13.5% protein was adequate in order to achieve normal production. The supplemented seed mix, containing 13.4% protein resulted in a highly significant reduction in performance. Seed mixtures tend to be deficient in amino acids, and despite the fact that vitamin and minerals were supplemented, this did rectify the shortfall. The lesson to be learned from this experiment, is that if the diet is fundamentally unsound (imbalanced), no amount of supplementation with vitamins or minerals will help.