7 Fig. 7.1 shows the percentage of different nutrients in a sample of freshly cut Napier grass and in a sample of Napier grass silage made from the same cro...

(a) Two differences between fresh grass and silage nutrient content [2]

From Fig. 7.1 (bar chart), any two valid comparative statements:

1. Silage has a higher crude protein (CP) percentage on a dry matter basis (10.2%) than fresh grass (8.5%). [1]
2. Fresh grass has a higher crude fibre (CF) content (32%) than silage (30.5%). [1]

Other acceptable: silage has higher fat (3.0% vs 2.1%); silage has higher ash (12.8% vs 11.0%).

(b) How silage is made from freshly cut grass [4]

1. The grass is cut at the correct stage of growth, ideally before flowering when nutrient content is highest. [1]
2. It is chopped into short lengths (2-5 cm) to aid compaction and create a uniform mass. [1]
3. The chopped grass is packed tightly into a pit, silo, or bunker and sealed with a polythene sheet to exclude air (creating anaerobic conditions). [1]
4. Under anaerobic conditions, lactic acid bacteria naturally present on the grass ferment soluble sugars, producing lactic acid. This lowers the pH (to about 4.0) and preserves the forage by inhibiting spoilage organisms. [1]

(c) One additive to improve silage quality [1]

Any one of:

• Molasses - provides extra sugar to fuel lactic acid fermentation, improving preservation. [1]
• A bacterial inoculant (e.g. Lactobacillus culture) - increases the population of desirable bacteria for faster, more efficient fermentation.
• Formic acid - directly lowers pH and inhibits undesirable organisms.
• Salt - helps preserve the silage.

(d) Two advantages of silage over hay [2]

Any two of:

1. Silage can be made in wet weather because it does not depend on dry, sunny conditions for field drying, unlike hay. [1]
2. Silage retains more nutrients than hay, because hay-making involves prolonged sun exposure that causes leaf shatter and nutrient loss. [1]
3. Silage can be made from a wider range of crops and grasses, including those that are difficult to dry as hay.
4. Silage stores well for long periods if properly sealed.

(e) Why crude protein percentage is higher in silage than fresh grass [2]

1. During ensiling, the loss of soluble carbohydrates (sugars) through fermentation reduces the total dry matter, but protein is not fermented to the same extent. [1]
2. Because the dry matter decreases proportionally more than the protein content, the protein expressed as a percentage of the remaining dry matter increases (a concentration effect). [1]

(f) One disadvantage of feeding poorly made silage [1]

Any one of:

• It can cause digestive problems such as bloat or scouring (diarrhoea) in animals. [1]
• Poorly fermented silage may contain harmful moulds, toxins, or butyric acid that reduce animal health and performance.
• Animals may refuse to eat it because of low palatability (foul smell, slimy texture).

(g) Name of the process converting sugars to lactic acid [1]

Fermentation (specifically anaerobic fermentation). [1] Lactic acid bacteria carry out this process in the absence of oxygen, converting plant sugars into lactic acid as their metabolic end-product.